lguest: documentation II: Guest
Documentation: The Guest Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -66,6 +66,12 @@
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#include <asm/mce.h>
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#include <asm/io.h>
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/*G:010 Welcome to the Guest!
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*
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* The Guest in our tale is a simple creature: identical to the Host but
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* behaving in simplified but equivalent ways. In particular, the Guest is the
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* same kernel as the Host (or at least, built from the same source code). :*/
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/* Declarations for definitions in lguest_guest.S */
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extern char lguest_noirq_start[], lguest_noirq_end[];
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extern const char lgstart_cli[], lgend_cli[];
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@ -84,7 +90,26 @@ struct lguest_data lguest_data = {
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struct lguest_device_desc *lguest_devices;
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static cycle_t clock_base;
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static enum paravirt_lazy_mode lazy_mode;
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/*G:035 Notice the lazy_hcall() above, rather than hcall(). This is our first
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* real optimization trick!
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*
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* When lazy_mode is set, it means we're allowed to defer all hypercalls and do
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* them as a batch when lazy_mode is eventually turned off. Because hypercalls
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* are reasonably expensive, batching them up makes sense. For example, a
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* large mmap might update dozens of page table entries: that code calls
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* lguest_lazy_mode(PARAVIRT_LAZY_MMU), does the dozen updates, then calls
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* lguest_lazy_mode(PARAVIRT_LAZY_NONE).
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*
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* So, when we're in lazy mode, we call async_hypercall() to store the call for
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* future processing. When lazy mode is turned off we issue a hypercall to
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* flush the stored calls.
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*
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* There's also a hack where "mode" is set to "PARAVIRT_LAZY_FLUSH" which
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* indicates we're to flush any outstanding calls immediately. This is used
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* when an interrupt handler does a kmap_atomic(): the page table changes must
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* happen immediately even if we're in the middle of a batch. Usually we're
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* not, though, so there's nothing to do. */
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static enum paravirt_lazy_mode lazy_mode; /* Note: not SMP-safe! */
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static void lguest_lazy_mode(enum paravirt_lazy_mode mode)
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{
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if (mode == PARAVIRT_LAZY_FLUSH) {
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@ -108,6 +133,16 @@ static void lazy_hcall(unsigned long call,
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async_hcall(call, arg1, arg2, arg3);
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}
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/* async_hcall() is pretty simple: I'm quite proud of it really. We have a
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* ring buffer of stored hypercalls which the Host will run though next time we
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* do a normal hypercall. Each entry in the ring has 4 slots for the hypercall
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* arguments, and a "hcall_status" word which is 0 if the call is ready to go,
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* and 255 once the Host has finished with it.
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*
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* If we come around to a slot which hasn't been finished, then the table is
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* full and we just make the hypercall directly. This has the nice side
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* effect of causing the Host to run all the stored calls in the ring buffer
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* which empties it for next time! */
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void async_hcall(unsigned long call,
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unsigned long arg1, unsigned long arg2, unsigned long arg3)
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{
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@ -115,6 +150,9 @@ void async_hcall(unsigned long call,
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static unsigned int next_call;
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unsigned long flags;
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/* Disable interrupts if not already disabled: we don't want an
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* interrupt handler making a hypercall while we're already doing
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* one! */
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local_irq_save(flags);
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if (lguest_data.hcall_status[next_call] != 0xFF) {
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/* Table full, so do normal hcall which will flush table. */
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@ -124,7 +162,7 @@ void async_hcall(unsigned long call,
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lguest_data.hcalls[next_call].edx = arg1;
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lguest_data.hcalls[next_call].ebx = arg2;
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lguest_data.hcalls[next_call].ecx = arg3;
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/* Make sure host sees arguments before "valid" flag. */
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/* Arguments must all be written before we mark it to go */
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wmb();
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lguest_data.hcall_status[next_call] = 0;
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if (++next_call == LHCALL_RING_SIZE)
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@ -132,9 +170,14 @@ void async_hcall(unsigned long call,
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}
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local_irq_restore(flags);
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}
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/*:*/
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/* Wrappers for the SEND_DMA and BIND_DMA hypercalls. This is mainly because
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* Jeff Garzik complained that __pa() should never appear in drivers, and this
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* helps remove most of them. But also, it wraps some ugliness. */
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void lguest_send_dma(unsigned long key, struct lguest_dma *dma)
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{
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/* The hcall might not write this if something goes wrong */
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dma->used_len = 0;
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hcall(LHCALL_SEND_DMA, key, __pa(dma), 0);
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}
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@ -142,11 +185,16 @@ void lguest_send_dma(unsigned long key, struct lguest_dma *dma)
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int lguest_bind_dma(unsigned long key, struct lguest_dma *dmas,
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unsigned int num, u8 irq)
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{
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/* This is the only hypercall which actually wants 5 arguments, and we
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* only support 4. Fortunately the interrupt number is always less
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* than 256, so we can pack it with the number of dmas in the final
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* argument. */
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if (!hcall(LHCALL_BIND_DMA, key, __pa(dmas), (num << 8) | irq))
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return -ENOMEM;
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return 0;
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}
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/* Unbinding is the same hypercall as binding, but with 0 num & irq. */
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void lguest_unbind_dma(unsigned long key, struct lguest_dma *dmas)
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{
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hcall(LHCALL_BIND_DMA, key, __pa(dmas), 0);
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@ -164,35 +212,65 @@ void lguest_unmap(void *addr)
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iounmap((__force void __iomem *)addr);
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}
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/*G:033
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* Here are our first native-instruction replacements: four functions for
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* interrupt control.
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*
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* The simplest way of implementing these would be to have "turn interrupts
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* off" and "turn interrupts on" hypercalls. Unfortunately, this is too slow:
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* these are by far the most commonly called functions of those we override.
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*
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* So instead we keep an "irq_enabled" field inside our "struct lguest_data",
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* which the Guest can update with a single instruction. The Host knows to
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* check there when it wants to deliver an interrupt.
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*/
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/* save_flags() is expected to return the processor state (ie. "eflags"). The
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* eflags word contains all kind of stuff, but in practice Linux only cares
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* about the interrupt flag. Our "save_flags()" just returns that. */
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static unsigned long save_fl(void)
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{
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return lguest_data.irq_enabled;
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}
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/* "restore_flags" just sets the flags back to the value given. */
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static void restore_fl(unsigned long flags)
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{
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/* FIXME: Check if interrupt pending... */
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lguest_data.irq_enabled = flags;
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}
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/* Interrupts go off... */
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static void irq_disable(void)
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{
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lguest_data.irq_enabled = 0;
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}
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/* Interrupts go on... */
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static void irq_enable(void)
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{
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/* FIXME: Check if interrupt pending... */
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lguest_data.irq_enabled = X86_EFLAGS_IF;
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}
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/*G:034
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* The Interrupt Descriptor Table (IDT).
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*
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* The IDT tells the processor what to do when an interrupt comes in. Each
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* entry in the table is a 64-bit descriptor: this holds the privilege level,
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* address of the handler, and... well, who cares? The Guest just asks the
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* Host to make the change anyway, because the Host controls the real IDT.
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*/
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static void lguest_write_idt_entry(struct desc_struct *dt,
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int entrynum, u32 low, u32 high)
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{
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/* Keep the local copy up to date. */
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write_dt_entry(dt, entrynum, low, high);
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/* Tell Host about this new entry. */
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hcall(LHCALL_LOAD_IDT_ENTRY, entrynum, low, high);
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}
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/* Changing to a different IDT is very rare: we keep the IDT up-to-date every
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* time it is written, so we can simply loop through all entries and tell the
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* Host about them. */
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static void lguest_load_idt(const struct Xgt_desc_struct *desc)
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{
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unsigned int i;
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hcall(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b);
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}
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/*
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* The Global Descriptor Table.
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*
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* The Intel architecture defines another table, called the Global Descriptor
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* Table (GDT). You tell the CPU where it is (and its size) using the "lgdt"
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* instruction, and then several other instructions refer to entries in the
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* table. There are three entries which the Switcher needs, so the Host simply
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* controls the entire thing and the Guest asks it to make changes using the
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* LOAD_GDT hypercall.
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*
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* This is the opposite of the IDT code where we have a LOAD_IDT_ENTRY
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* hypercall and use that repeatedly to load a new IDT. I don't think it
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* really matters, but wouldn't it be nice if they were the same?
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*/
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static void lguest_load_gdt(const struct Xgt_desc_struct *desc)
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{
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BUG_ON((desc->size+1)/8 != GDT_ENTRIES);
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hcall(LHCALL_LOAD_GDT, __pa(desc->address), GDT_ENTRIES, 0);
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}
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/* For a single GDT entry which changes, we do the lazy thing: alter our GDT,
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* then tell the Host to reload the entire thing. This operation is so rare
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* that this naive implementation is reasonable. */
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static void lguest_write_gdt_entry(struct desc_struct *dt,
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int entrynum, u32 low, u32 high)
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{
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hcall(LHCALL_LOAD_GDT, __pa(dt), GDT_ENTRIES, 0);
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}
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/* OK, I lied. There are three "thread local storage" GDT entries which change
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* on every context switch (these three entries are how glibc implements
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* __thread variables). So we have a hypercall specifically for this case. */
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static void lguest_load_tls(struct thread_struct *t, unsigned int cpu)
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{
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lazy_hcall(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu, 0);
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}
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/*:*/
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/*G:038 That's enough excitement for now, back to ploughing through each of
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* the paravirt_ops (we're about 1/3 of the way through).
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*
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* This is the Local Descriptor Table, another weird Intel thingy. Linux only
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* uses this for some strange applications like Wine. We don't do anything
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* here, so they'll get an informative and friendly Segmentation Fault. */
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static void lguest_set_ldt(const void *addr, unsigned entries)
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{
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}
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/* This loads a GDT entry into the "Task Register": that entry points to a
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* structure called the Task State Segment. Some comments scattered though the
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* kernel code indicate that this used for task switching in ages past, along
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* with blood sacrifice and astrology.
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*
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* Now there's nothing interesting in here that we don't get told elsewhere.
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* But the native version uses the "ltr" instruction, which makes the Host
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* complain to the Guest about a Segmentation Fault and it'll oops. So we
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* override the native version with a do-nothing version. */
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static void lguest_load_tr_desc(void)
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{
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}
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/* The "cpuid" instruction is a way of querying both the CPU identity
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* (manufacturer, model, etc) and its features. It was introduced before the
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* Pentium in 1993 and keeps getting extended by both Intel and AMD. As you
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* might imagine, after a decade and a half this treatment, it is now a giant
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* ball of hair. Its entry in the current Intel manual runs to 28 pages.
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*
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* This instruction even it has its own Wikipedia entry. The Wikipedia entry
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* has been translated into 4 languages. I am not making this up!
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*
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* We could get funky here and identify ourselves as "GenuineLguest", but
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* instead we just use the real "cpuid" instruction. Then I pretty much turned
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* off feature bits until the Guest booted. (Don't say that: you'll damage
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* lguest sales!) Shut up, inner voice! (Hey, just pointing out that this is
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* hardly future proof.) Noone's listening! They don't like you anyway,
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* parenthetic weirdo!
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*
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* Replacing the cpuid so we can turn features off is great for the kernel, but
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* anyone (including userspace) can just use the raw "cpuid" instruction and
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* the Host won't even notice since it isn't privileged. So we try not to get
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* too worked up about it. */
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static void lguest_cpuid(unsigned int *eax, unsigned int *ebx,
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unsigned int *ecx, unsigned int *edx)
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{
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*ecx &= 0x00002201;
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/* SSE, SSE2, FXSR, MMX, CMOV, CMPXCHG8B, FPU. */
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*edx &= 0x07808101;
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/* Host wants to know when we flush kernel pages: set PGE. */
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/* The Host can do a nice optimization if it knows that the
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* kernel mappings (addresses above 0xC0000000 or whatever
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* PAGE_OFFSET is set to) haven't changed. But Linux calls
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* flush_tlb_user() for both user and kernel mappings unless
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* the Page Global Enable (PGE) feature bit is set. */
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*edx |= 0x00002000;
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break;
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case 0x80000000:
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/* Futureproof this a little: if they ask how much extended
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* processor information, limit it to known fields. */
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* processor information there is, limit it to known fields. */
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if (*eax > 0x80000008)
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*eax = 0x80000008;
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break;
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}
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}
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/* Intel has four control registers, imaginatively named cr0, cr2, cr3 and cr4.
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* I assume there's a cr1, but it hasn't bothered us yet, so we'll not bother
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* it. The Host needs to know when the Guest wants to change them, so we have
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* a whole series of functions like read_cr0() and write_cr0().
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*
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* We start with CR0. CR0 allows you to turn on and off all kinds of basic
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* features, but Linux only really cares about one: the horrifically-named Task
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* Switched (TS) bit at bit 3 (ie. 8)
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*
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* What does the TS bit do? Well, it causes the CPU to trap (interrupt 7) if
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* the floating point unit is used. Which allows us to restore FPU state
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* lazily after a task switch, and Linux uses that gratefully, but wouldn't a
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* name like "FPUTRAP bit" be a little less cryptic?
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*
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* We store cr0 (and cr3) locally, because the Host never changes it. The
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* Guest sometimes wants to read it and we'd prefer not to bother the Host
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* unnecessarily. */
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static unsigned long current_cr0, current_cr3;
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static void lguest_write_cr0(unsigned long val)
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{
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/* 8 == TS bit. */
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lazy_hcall(LHCALL_TS, val & 8, 0, 0);
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current_cr0 = val;
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}
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return current_cr0;
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}
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/* Intel provided a special instruction to clear the TS bit for people too cool
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* to use write_cr0() to do it. This "clts" instruction is faster, because all
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* the vowels have been optimized out. */
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static void lguest_clts(void)
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{
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lazy_hcall(LHCALL_TS, 0, 0, 0);
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current_cr0 &= ~8U;
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}
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/* CR2 is the virtual address of the last page fault, which the Guest only ever
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* reads. The Host kindly writes this into our "struct lguest_data", so we
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* just read it out of there. */
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static unsigned long lguest_read_cr2(void)
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{
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return lguest_data.cr2;
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}
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/* CR3 is the current toplevel pagetable page: the principle is the same as
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* cr0. Keep a local copy, and tell the Host when it changes. */
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static void lguest_write_cr3(unsigned long cr3)
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{
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lazy_hcall(LHCALL_NEW_PGTABLE, cr3, 0, 0);
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return current_cr3;
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}
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/* Used to enable/disable PGE, but we don't care. */
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/* CR4 is used to enable and disable PGE, but we don't care. */
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static unsigned long lguest_read_cr4(void)
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{
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return 0;
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@ -296,6 +460,59 @@ static void lguest_write_cr4(unsigned long val)
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{
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}
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/*
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* Page Table Handling.
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*
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* Now would be a good time to take a rest and grab a coffee or similarly
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* relaxing stimulant. The easy parts are behind us, and the trek gradually
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* winds uphill from here.
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*
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* Quick refresher: memory is divided into "pages" of 4096 bytes each. The CPU
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* maps virtual addresses to physical addresses using "page tables". We could
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* use one huge index of 1 million entries: each address is 4 bytes, so that's
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* 1024 pages just to hold the page tables. But since most virtual addresses
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* are unused, we use a two level index which saves space. The CR3 register
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* contains the physical address of the top level "page directory" page, which
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* contains physical addresses of up to 1024 second-level pages. Each of these
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* second level pages contains up to 1024 physical addresses of actual pages,
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* or Page Table Entries (PTEs).
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*
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* Here's a diagram, where arrows indicate physical addresses:
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*
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* CR3 ---> +---------+
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* | --------->+---------+
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* | | | PADDR1 |
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* Top-level | | PADDR2 |
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* (PMD) page | | |
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* | | Lower-level |
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* | | (PTE) page |
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* | | | |
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* .... ....
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*
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* So to convert a virtual address to a physical address, we look up the top
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* level, which points us to the second level, which gives us the physical
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* address of that page. If the top level entry was not present, or the second
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* level entry was not present, then the virtual address is invalid (we
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* say "the page was not mapped").
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*
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* Put another way, a 32-bit virtual address is divided up like so:
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*
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* 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
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* |<---- 10 bits ---->|<---- 10 bits ---->|<------ 12 bits ------>|
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* Index into top Index into second Offset within page
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* page directory page pagetable page
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*
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* The kernel spends a lot of time changing both the top-level page directory
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* and lower-level pagetable pages. The Guest doesn't know physical addresses,
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* so while it maintains these page tables exactly like normal, it also needs
|
||||
* to keep the Host informed whenever it makes a change: the Host will create
|
||||
* the real page tables based on the Guests'.
|
||||
*/
|
||||
|
||||
/* The Guest calls this to set a second-level entry (pte), ie. to map a page
|
||||
* into a process' address space. We set the entry then tell the Host the
|
||||
* toplevel and address this corresponds to. The Guest uses one pagetable per
|
||||
* process, so we need to tell the Host which one we're changing (mm->pgd). */
|
||||
static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
|
||||
pte_t *ptep, pte_t pteval)
|
||||
{
|
||||
|
@ -303,7 +520,9 @@ static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
|
|||
lazy_hcall(LHCALL_SET_PTE, __pa(mm->pgd), addr, pteval.pte_low);
|
||||
}
|
||||
|
||||
/* We only support two-level pagetables at the moment. */
|
||||
/* The Guest calls this to set a top-level entry. Again, we set the entry then
|
||||
* tell the Host which top-level page we changed, and the index of the entry we
|
||||
* changed. */
|
||||
static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
|
||||
{
|
||||
*pmdp = pmdval;
|
||||
|
@ -311,7 +530,15 @@ static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
|
|||
(__pa(pmdp)&(PAGE_SIZE-1))/4, 0);
|
||||
}
|
||||
|
||||
/* FIXME: Eliminate all callers of this. */
|
||||
/* There are a couple of legacy places where the kernel sets a PTE, but we
|
||||
* don't know the top level any more. This is useless for us, since we don't
|
||||
* know which pagetable is changing or what address, so we just tell the Host
|
||||
* to forget all of them. Fortunately, this is very rare.
|
||||
*
|
||||
* ... except in early boot when the kernel sets up the initial pagetables,
|
||||
* which makes booting astonishingly slow. So we don't even tell the Host
|
||||
* anything changed until we've done the first page table switch.
|
||||
*/
|
||||
static void lguest_set_pte(pte_t *ptep, pte_t pteval)
|
||||
{
|
||||
*ptep = pteval;
|
||||
|
@ -320,22 +547,51 @@ static void lguest_set_pte(pte_t *ptep, pte_t pteval)
|
|||
lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
|
||||
}
|
||||
|
||||
/* Unfortunately for Lguest, the paravirt_ops for page tables were based on
|
||||
* native page table operations. On native hardware you can set a new page
|
||||
* table entry whenever you want, but if you want to remove one you have to do
|
||||
* a TLB flush (a TLB is a little cache of page table entries kept by the CPU).
|
||||
*
|
||||
* So the lguest_set_pte_at() and lguest_set_pmd() functions above are only
|
||||
* called when a valid entry is written, not when it's removed (ie. marked not
|
||||
* present). Instead, this is where we come when the Guest wants to remove a
|
||||
* page table entry: we tell the Host to set that entry to 0 (ie. the present
|
||||
* bit is zero). */
|
||||
static void lguest_flush_tlb_single(unsigned long addr)
|
||||
{
|
||||
/* Simply set it to zero, and it will fault back in. */
|
||||
/* Simply set it to zero: if it was not, it will fault back in. */
|
||||
lazy_hcall(LHCALL_SET_PTE, current_cr3, addr, 0);
|
||||
}
|
||||
|
||||
/* This is what happens after the Guest has removed a large number of entries.
|
||||
* This tells the Host that any of the page table entries for userspace might
|
||||
* have changed, ie. virtual addresses below PAGE_OFFSET. */
|
||||
static void lguest_flush_tlb_user(void)
|
||||
{
|
||||
lazy_hcall(LHCALL_FLUSH_TLB, 0, 0, 0);
|
||||
}
|
||||
|
||||
/* This is called when the kernel page tables have changed. That's not very
|
||||
* common (unless the Guest is using highmem, which makes the Guest extremely
|
||||
* slow), so it's worth separating this from the user flushing above. */
|
||||
static void lguest_flush_tlb_kernel(void)
|
||||
{
|
||||
lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
|
||||
}
|
||||
|
||||
/*
|
||||
* The Unadvanced Programmable Interrupt Controller.
|
||||
*
|
||||
* This is an attempt to implement the simplest possible interrupt controller.
|
||||
* I spent some time looking though routines like set_irq_chip_and_handler,
|
||||
* set_irq_chip_and_handler_name, set_irq_chip_data and set_phasers_to_stun and
|
||||
* I *think* this is as simple as it gets.
|
||||
*
|
||||
* We can tell the Host what interrupts we want blocked ready for using the
|
||||
* lguest_data.interrupts bitmap, so disabling (aka "masking") them is as
|
||||
* simple as setting a bit. We don't actually "ack" interrupts as such, we
|
||||
* just mask and unmask them. I wonder if we should be cleverer?
|
||||
*/
|
||||
static void disable_lguest_irq(unsigned int irq)
|
||||
{
|
||||
set_bit(irq, lguest_data.blocked_interrupts);
|
||||
|
@ -344,9 +600,9 @@ static void disable_lguest_irq(unsigned int irq)
|
|||
static void enable_lguest_irq(unsigned int irq)
|
||||
{
|
||||
clear_bit(irq, lguest_data.blocked_interrupts);
|
||||
/* FIXME: If it's pending? */
|
||||
}
|
||||
|
||||
/* This structure describes the lguest IRQ controller. */
|
||||
static struct irq_chip lguest_irq_controller = {
|
||||
.name = "lguest",
|
||||
.mask = disable_lguest_irq,
|
||||
|
@ -354,6 +610,10 @@ static struct irq_chip lguest_irq_controller = {
|
|||
.unmask = enable_lguest_irq,
|
||||
};
|
||||
|
||||
/* This sets up the Interrupt Descriptor Table (IDT) entry for each hardware
|
||||
* interrupt (except 128, which is used for system calls), and then tells the
|
||||
* Linux infrastructure that each interrupt is controlled by our level-based
|
||||
* lguest interrupt controller. */
|
||||
static void __init lguest_init_IRQ(void)
|
||||
{
|
||||
unsigned int i;
|
||||
|
@ -366,14 +626,24 @@ static void __init lguest_init_IRQ(void)
|
|||
handle_level_irq);
|
||||
}
|
||||
}
|
||||
/* This call is required to set up for 4k stacks, where we have
|
||||
* separate stacks for hard and soft interrupts. */
|
||||
irq_ctx_init(smp_processor_id());
|
||||
}
|
||||
|
||||
/*
|
||||
* Time.
|
||||
*
|
||||
* It would be far better for everyone if the Guest had its own clock, but
|
||||
* until then it must ask the Host for the time.
|
||||
*/
|
||||
static unsigned long lguest_get_wallclock(void)
|
||||
{
|
||||
return hcall(LHCALL_GET_WALLCLOCK, 0, 0, 0);
|
||||
}
|
||||
|
||||
/* If the Host tells us we can trust the TSC, we use that, otherwise we simply
|
||||
* use the imprecise but reliable "jiffies" counter. */
|
||||
static cycle_t lguest_clock_read(void)
|
||||
{
|
||||
if (lguest_data.tsc_khz)
|
||||
|
@ -454,12 +724,19 @@ static void lguest_time_irq(unsigned int irq, struct irq_desc *desc)
|
|||
local_irq_restore(flags);
|
||||
}
|
||||
|
||||
/* At some point in the boot process, we get asked to set up our timing
|
||||
* infrastructure. The kernel doesn't expect timer interrupts before this, but
|
||||
* we cleverly initialized the "blocked_interrupts" field of "struct
|
||||
* lguest_data" so that timer interrupts were blocked until now. */
|
||||
static void lguest_time_init(void)
|
||||
{
|
||||
/* Set up the timer interrupt (0) to go to our simple timer routine */
|
||||
set_irq_handler(0, lguest_time_irq);
|
||||
|
||||
/* We use the TSC if the Host tells us we can, otherwise a dumb
|
||||
* jiffies-based clock. */
|
||||
/* Our clock structure look like arch/i386/kernel/tsc.c if we can use
|
||||
* the TSC, otherwise it looks like kernel/time/jiffies.c. Either way,
|
||||
* the "rating" is initialized so high that it's always chosen over any
|
||||
* other clocksource. */
|
||||
if (lguest_data.tsc_khz) {
|
||||
lguest_clock.shift = 22;
|
||||
lguest_clock.mult = clocksource_khz2mult(lguest_data.tsc_khz,
|
||||
|
@ -475,13 +752,30 @@ static void lguest_time_init(void)
|
|||
clock_base = lguest_clock_read();
|
||||
clocksource_register(&lguest_clock);
|
||||
|
||||
/* We can't set cpumask in the initializer: damn C limitations! */
|
||||
/* We can't set cpumask in the initializer: damn C limitations! Set it
|
||||
* here and register our timer device. */
|
||||
lguest_clockevent.cpumask = cpumask_of_cpu(0);
|
||||
clockevents_register_device(&lguest_clockevent);
|
||||
|
||||
/* Finally, we unblock the timer interrupt. */
|
||||
enable_lguest_irq(0);
|
||||
}
|
||||
|
||||
/*
|
||||
* Miscellaneous bits and pieces.
|
||||
*
|
||||
* Here is an oddball collection of functions which the Guest needs for things
|
||||
* to work. They're pretty simple.
|
||||
*/
|
||||
|
||||
/* The Guest needs to tell the host what stack it expects traps to use. For
|
||||
* native hardware, this is part of the Task State Segment mentioned above in
|
||||
* lguest_load_tr_desc(), but to help hypervisors there's this special call.
|
||||
*
|
||||
* We tell the Host the segment we want to use (__KERNEL_DS is the kernel data
|
||||
* segment), the privilege level (we're privilege level 1, the Host is 0 and
|
||||
* will not tolerate us trying to use that), the stack pointer, and the number
|
||||
* of pages in the stack. */
|
||||
static void lguest_load_esp0(struct tss_struct *tss,
|
||||
struct thread_struct *thread)
|
||||
{
|
||||
|
@ -489,15 +783,31 @@ static void lguest_load_esp0(struct tss_struct *tss,
|
|||
THREAD_SIZE/PAGE_SIZE);
|
||||
}
|
||||
|
||||
/* Let's just say, I wouldn't do debugging under a Guest. */
|
||||
static void lguest_set_debugreg(int regno, unsigned long value)
|
||||
{
|
||||
/* FIXME: Implement */
|
||||
}
|
||||
|
||||
/* There are times when the kernel wants to make sure that no memory writes are
|
||||
* caught in the cache (that they've all reached real hardware devices). This
|
||||
* doesn't matter for the Guest which has virtual hardware.
|
||||
*
|
||||
* On the Pentium 4 and above, cpuid() indicates that the Cache Line Flush
|
||||
* (clflush) instruction is available and the kernel uses that. Otherwise, it
|
||||
* uses the older "Write Back and Invalidate Cache" (wbinvd) instruction.
|
||||
* Unlike clflush, wbinvd can only be run at privilege level 0. So we can
|
||||
* ignore clflush, but replace wbinvd.
|
||||
*/
|
||||
static void lguest_wbinvd(void)
|
||||
{
|
||||
}
|
||||
|
||||
/* If the Guest expects to have an Advanced Programmable Interrupt Controller,
|
||||
* we play dumb by ignoring writes and returning 0 for reads. So it's no
|
||||
* longer Programmable nor Controlling anything, and I don't think 8 lines of
|
||||
* code qualifies for Advanced. It will also never interrupt anything. It
|
||||
* does, however, allow us to get through the Linux boot code. */
|
||||
#ifdef CONFIG_X86_LOCAL_APIC
|
||||
static void lguest_apic_write(unsigned long reg, unsigned long v)
|
||||
{
|
||||
|
@ -509,19 +819,32 @@ static unsigned long lguest_apic_read(unsigned long reg)
|
|||
}
|
||||
#endif
|
||||
|
||||
/* STOP! Until an interrupt comes in. */
|
||||
static void lguest_safe_halt(void)
|
||||
{
|
||||
hcall(LHCALL_HALT, 0, 0, 0);
|
||||
}
|
||||
|
||||
/* Perhaps CRASH isn't the best name for this hypercall, but we use it to get a
|
||||
* message out when we're crashing as well as elegant termination like powering
|
||||
* off.
|
||||
*
|
||||
* Note that the Host always prefers that the Guest speak in physical addresses
|
||||
* rather than virtual addresses, so we use __pa() here. */
|
||||
static void lguest_power_off(void)
|
||||
{
|
||||
hcall(LHCALL_CRASH, __pa("Power down"), 0, 0);
|
||||
}
|
||||
|
||||
/*
|
||||
* Panicing.
|
||||
*
|
||||
* Don't. But if you did, this is what happens.
|
||||
*/
|
||||
static int lguest_panic(struct notifier_block *nb, unsigned long l, void *p)
|
||||
{
|
||||
hcall(LHCALL_CRASH, __pa(p), 0, 0);
|
||||
/* The hcall won't return, but to keep gcc happy, we're "done". */
|
||||
return NOTIFY_DONE;
|
||||
}
|
||||
|
||||
|
@ -529,15 +852,45 @@ static struct notifier_block paniced = {
|
|||
.notifier_call = lguest_panic
|
||||
};
|
||||
|
||||
/* Setting up memory is fairly easy. */
|
||||
static __init char *lguest_memory_setup(void)
|
||||
{
|
||||
/* We do this here because lockcheck barfs if before start_kernel */
|
||||
/* We do this here and not earlier because lockcheck barfs if we do it
|
||||
* before start_kernel() */
|
||||
atomic_notifier_chain_register(&panic_notifier_list, &paniced);
|
||||
|
||||
/* The Linux bootloader header contains an "e820" memory map: the
|
||||
* Launcher populated the first entry with our memory limit. */
|
||||
add_memory_region(E820_MAP->addr, E820_MAP->size, E820_MAP->type);
|
||||
|
||||
/* This string is for the boot messages. */
|
||||
return "LGUEST";
|
||||
}
|
||||
|
||||
/*G:050
|
||||
* Patching (Powerfully Placating Performance Pedants)
|
||||
*
|
||||
* We have already seen that "struct paravirt_ops" lets us replace simple
|
||||
* native instructions with calls to the appropriate back end all throughout
|
||||
* the kernel. This allows the same kernel to run as a Guest and as a native
|
||||
* kernel, but it's slow because of all the indirect branches.
|
||||
*
|
||||
* Remember that David Wheeler quote about "Any problem in computer science can
|
||||
* be solved with another layer of indirection"? The rest of that quote is
|
||||
* "... But that usually will create another problem." This is the first of
|
||||
* those problems.
|
||||
*
|
||||
* Our current solution is to allow the paravirt back end to optionally patch
|
||||
* over the indirect calls to replace them with something more efficient. We
|
||||
* patch the four most commonly called functions: disable interrupts, enable
|
||||
* interrupts, restore interrupts and save interrupts. We usually have 10
|
||||
* bytes to patch into: the Guest versions of these operations are small enough
|
||||
* that we can fit comfortably.
|
||||
*
|
||||
* First we need assembly templates of each of the patchable Guest operations,
|
||||
* and these are in lguest_asm.S. */
|
||||
|
||||
/*G:060 We construct a table from the assembler templates: */
|
||||
static const struct lguest_insns
|
||||
{
|
||||
const char *start, *end;
|
||||
|
@ -547,35 +900,52 @@ static const struct lguest_insns
|
|||
[PARAVIRT_PATCH(restore_fl)] = { lgstart_popf, lgend_popf },
|
||||
[PARAVIRT_PATCH(save_fl)] = { lgstart_pushf, lgend_pushf },
|
||||
};
|
||||
|
||||
/* Now our patch routine is fairly simple (based on the native one in
|
||||
* paravirt.c). If we have a replacement, we copy it in and return how much of
|
||||
* the available space we used. */
|
||||
static unsigned lguest_patch(u8 type, u16 clobber, void *insns, unsigned len)
|
||||
{
|
||||
unsigned int insn_len;
|
||||
|
||||
/* Don't touch it if we don't have a replacement */
|
||||
/* Don't do anything special if we don't have a replacement */
|
||||
if (type >= ARRAY_SIZE(lguest_insns) || !lguest_insns[type].start)
|
||||
return paravirt_patch_default(type, clobber, insns, len);
|
||||
|
||||
insn_len = lguest_insns[type].end - lguest_insns[type].start;
|
||||
|
||||
/* Similarly if we can't fit replacement. */
|
||||
/* Similarly if we can't fit replacement (shouldn't happen, but let's
|
||||
* be thorough). */
|
||||
if (len < insn_len)
|
||||
return paravirt_patch_default(type, clobber, insns, len);
|
||||
|
||||
/* Copy in our instructions. */
|
||||
memcpy(insns, lguest_insns[type].start, insn_len);
|
||||
return insn_len;
|
||||
}
|
||||
|
||||
/*G:030 Once we get to lguest_init(), we know we're a Guest. The paravirt_ops
|
||||
* structure in the kernel provides a single point for (almost) every routine
|
||||
* we have to override to avoid privileged instructions. */
|
||||
__init void lguest_init(void *boot)
|
||||
{
|
||||
/* Copy boot parameters first. */
|
||||
/* Copy boot parameters first: the Launcher put the physical location
|
||||
* in %esi, and head.S converted that to a virtual address and handed
|
||||
* it to us. */
|
||||
memcpy(&boot_params, boot, PARAM_SIZE);
|
||||
/* The boot parameters also tell us where the command-line is: save
|
||||
* that, too. */
|
||||
memcpy(boot_command_line, __va(boot_params.hdr.cmd_line_ptr),
|
||||
COMMAND_LINE_SIZE);
|
||||
|
||||
/* We're under lguest, paravirt is enabled, and we're running at
|
||||
* privilege level 1, not 0 as normal. */
|
||||
paravirt_ops.name = "lguest";
|
||||
paravirt_ops.paravirt_enabled = 1;
|
||||
paravirt_ops.kernel_rpl = 1;
|
||||
|
||||
/* We set up all the lguest overrides for sensitive operations. These
|
||||
* are detailed with the operations themselves. */
|
||||
paravirt_ops.save_fl = save_fl;
|
||||
paravirt_ops.restore_fl = restore_fl;
|
||||
paravirt_ops.irq_disable = irq_disable;
|
||||
|
@ -619,20 +989,45 @@ __init void lguest_init(void *boot)
|
|||
paravirt_ops.set_lazy_mode = lguest_lazy_mode;
|
||||
paravirt_ops.wbinvd = lguest_wbinvd;
|
||||
paravirt_ops.sched_clock = lguest_sched_clock;
|
||||
/* Now is a good time to look at the implementations of these functions
|
||||
* before returning to the rest of lguest_init(). */
|
||||
|
||||
/*G:070 Now we've seen all the paravirt_ops, we return to
|
||||
* lguest_init() where the rest of the fairly chaotic boot setup
|
||||
* occurs.
|
||||
*
|
||||
* The Host expects our first hypercall to tell it where our "struct
|
||||
* lguest_data" is, so we do that first. */
|
||||
hcall(LHCALL_LGUEST_INIT, __pa(&lguest_data), 0, 0);
|
||||
|
||||
/* We use top of mem for initial pagetables. */
|
||||
/* The native boot code sets up initial page tables immediately after
|
||||
* the kernel itself, and sets init_pg_tables_end so they're not
|
||||
* clobbered. The Launcher places our initial pagetables somewhere at
|
||||
* the top of our physical memory, so we don't need extra space: set
|
||||
* init_pg_tables_end to the end of the kernel. */
|
||||
init_pg_tables_end = __pa(pg0);
|
||||
|
||||
/* Load the %fs segment register (the per-cpu segment register) with
|
||||
* the normal data segment to get through booting. */
|
||||
asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_DS) : "memory");
|
||||
|
||||
/* The Host uses the top of the Guest's virtual address space for the
|
||||
* Host<->Guest Switcher, and it tells us how much it needs in
|
||||
* lguest_data.reserve_mem, set up on the LGUEST_INIT hypercall. */
|
||||
reserve_top_address(lguest_data.reserve_mem);
|
||||
|
||||
/* If we don't initialize the lock dependency checker now, it crashes
|
||||
* paravirt_disable_iospace. */
|
||||
lockdep_init();
|
||||
|
||||
/* The IDE code spends about 3 seconds probing for disks: if we reserve
|
||||
* all the I/O ports up front it can't get them and so doesn't probe.
|
||||
* Other device drivers are similar (but less severe). This cuts the
|
||||
* kernel boot time on my machine from 4.1 seconds to 0.45 seconds. */
|
||||
paravirt_disable_iospace();
|
||||
|
||||
/* This is messy CPU setup stuff which the native boot code does before
|
||||
* start_kernel, so we have to do, too: */
|
||||
cpu_detect(&new_cpu_data);
|
||||
/* head.S usually sets up the first capability word, so do it here. */
|
||||
new_cpu_data.x86_capability[0] = cpuid_edx(1);
|
||||
|
@ -643,14 +1038,27 @@ __init void lguest_init(void *boot)
|
|||
#ifdef CONFIG_X86_MCE
|
||||
mce_disabled = 1;
|
||||
#endif
|
||||
|
||||
#ifdef CONFIG_ACPI
|
||||
acpi_disabled = 1;
|
||||
acpi_ht = 0;
|
||||
#endif
|
||||
|
||||
/* We set the perferred console to "hvc". This is the "hypervisor
|
||||
* virtual console" driver written by the PowerPC people, which we also
|
||||
* adapted for lguest's use. */
|
||||
add_preferred_console("hvc", 0, NULL);
|
||||
|
||||
/* Last of all, we set the power management poweroff hook to point to
|
||||
* the Guest routine to power off. */
|
||||
pm_power_off = lguest_power_off;
|
||||
|
||||
/* Now we're set up, call start_kernel() in init/main.c and we proceed
|
||||
* to boot as normal. It never returns. */
|
||||
start_kernel();
|
||||
}
|
||||
/*
|
||||
* This marks the end of stage II of our journey, The Guest.
|
||||
*
|
||||
* It is now time for us to explore the nooks and crannies of the three Guest
|
||||
* devices and complete our understanding of the Guest in "make Drivers".
|
||||
*/
|
||||
|
|
|
@ -4,15 +4,15 @@
|
|||
#include <asm/thread_info.h>
|
||||
#include <asm/processor-flags.h>
|
||||
|
||||
/*
|
||||
* This is where we begin: we have a magic signature which the launcher looks
|
||||
* for. The plan is that the Linux boot protocol will be extended with a
|
||||
/*G:020 This is where we begin: we have a magic signature which the launcher
|
||||
* looks for. The plan is that the Linux boot protocol will be extended with a
|
||||
* "platform type" field which will guide us here from the normal entry point,
|
||||
* but for the moment this suffices. We pass the virtual address of the boot
|
||||
* info to lguest_init().
|
||||
* but for the moment this suffices. The normal boot code uses %esi for the
|
||||
* boot header, so we do too. We convert it to a virtual address by adding
|
||||
* PAGE_OFFSET, and hand it to lguest_init() as its argument (ie. %eax).
|
||||
*
|
||||
* We put it in .init.text will be discarded after boot.
|
||||
*/
|
||||
* The .section line puts this code in .init.text so it will be discarded after
|
||||
* boot. */
|
||||
.section .init.text, "ax", @progbits
|
||||
.ascii "GenuineLguest"
|
||||
/* Set up initial stack. */
|
||||
|
@ -21,7 +21,9 @@
|
|||
addl $__PAGE_OFFSET, %eax
|
||||
jmp lguest_init
|
||||
|
||||
/* The templates for inline patching. */
|
||||
/*G:055 We create a macro which puts the assembler code between lgstart_ and
|
||||
* lgend_ markers. These templates end up in the .init.text section, so they
|
||||
* are discarded after boot. */
|
||||
#define LGUEST_PATCH(name, insns...) \
|
||||
lgstart_##name: insns; lgend_##name:; \
|
||||
.globl lgstart_##name; .globl lgend_##name
|
||||
|
@ -30,24 +32,47 @@ LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled)
|
|||
LGUEST_PATCH(sti, movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled)
|
||||
LGUEST_PATCH(popf, movl %eax, lguest_data+LGUEST_DATA_irq_enabled)
|
||||
LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax)
|
||||
/*:*/
|
||||
|
||||
.text
|
||||
/* These demark the EIP range where host should never deliver interrupts. */
|
||||
.global lguest_noirq_start
|
||||
.global lguest_noirq_end
|
||||
|
||||
/*
|
||||
* We move eflags word to lguest_data.irq_enabled to restore interrupt state.
|
||||
* For page faults, gpfs and virtual interrupts, the hypervisor has saved
|
||||
* eflags manually, otherwise it was delivered directly and so eflags reflects
|
||||
* the real machine IF state, ie. interrupts on. Since the kernel always dies
|
||||
* if it takes such a trap with interrupts disabled anyway, turning interrupts
|
||||
* back on unconditionally here is OK.
|
||||
*/
|
||||
/*G:045 There is one final paravirt_op that the Guest implements, and glancing
|
||||
* at it you can see why I left it to last. It's *cool*! It's in *assembler*!
|
||||
*
|
||||
* The "iret" instruction is used to return from an interrupt or trap. The
|
||||
* stack looks like this:
|
||||
* old address
|
||||
* old code segment & privilege level
|
||||
* old processor flags ("eflags")
|
||||
*
|
||||
* The "iret" instruction pops those values off the stack and restores them all
|
||||
* at once. The only problem is that eflags includes the Interrupt Flag which
|
||||
* the Guest can't change: the CPU will simply ignore it when we do an "iret".
|
||||
* So we have to copy eflags from the stack to lguest_data.irq_enabled before
|
||||
* we do the "iret".
|
||||
*
|
||||
* There are two problems with this: firstly, we need to use a register to do
|
||||
* the copy and secondly, the whole thing needs to be atomic. The first
|
||||
* problem is easy to solve: push %eax on the stack so we can use it, and then
|
||||
* restore it at the end just before the real "iret".
|
||||
*
|
||||
* The second is harder: copying eflags to lguest_data.irq_enabled will turn
|
||||
* interrupts on before we're finished, so we could be interrupted before we
|
||||
* return to userspace or wherever. Our solution to this is to surround the
|
||||
* code with lguest_noirq_start: and lguest_noirq_end: labels. We tell the
|
||||
* Host that it is *never* to interrupt us there, even if interrupts seem to be
|
||||
* enabled. */
|
||||
ENTRY(lguest_iret)
|
||||
pushl %eax
|
||||
movl 12(%esp), %eax
|
||||
lguest_noirq_start:
|
||||
/* Note the %ss: segment prefix here. Normal data accesses use the
|
||||
* "ds" segment, but that will have already been restored for whatever
|
||||
* we're returning to (such as userspace): we can't trust it. The %ss:
|
||||
* prefix makes sure we use the stack segment, which is still valid. */
|
||||
movl %eax,%ss:lguest_data+LGUEST_DATA_irq_enabled
|
||||
popl %eax
|
||||
iret
|
||||
|
|
|
@ -27,18 +27,38 @@
|
|||
#define LG_CLOCK_MIN_DELTA 100UL
|
||||
#define LG_CLOCK_MAX_DELTA ULONG_MAX
|
||||
|
||||
/*G:031 First, how does our Guest contact the Host to ask for privileged
|
||||
* operations? There are two ways: the direct way is to make a "hypercall",
|
||||
* to make requests of the Host Itself.
|
||||
*
|
||||
* Our hypercall mechanism uses the highest unused trap code (traps 32 and
|
||||
* above are used by real hardware interrupts). Seventeen hypercalls are
|
||||
* available: the hypercall number is put in the %eax register, and the
|
||||
* arguments (when required) are placed in %edx, %ebx and %ecx. If a return
|
||||
* value makes sense, it's returned in %eax.
|
||||
*
|
||||
* Grossly invalid calls result in Sudden Death at the hands of the vengeful
|
||||
* Host, rather than returning failure. This reflects Winston Churchill's
|
||||
* definition of a gentleman: "someone who is only rude intentionally". */
|
||||
#define LGUEST_TRAP_ENTRY 0x1F
|
||||
|
||||
static inline unsigned long
|
||||
hcall(unsigned long call,
|
||||
unsigned long arg1, unsigned long arg2, unsigned long arg3)
|
||||
{
|
||||
/* "int" is the Intel instruction to trigger a trap. */
|
||||
asm volatile("int $" __stringify(LGUEST_TRAP_ENTRY)
|
||||
/* The call is in %eax (aka "a"), and can be replaced */
|
||||
: "=a"(call)
|
||||
/* The other arguments are in %eax, %edx, %ebx & %ecx */
|
||||
: "a"(call), "d"(arg1), "b"(arg2), "c"(arg3)
|
||||
/* "memory" means this might write somewhere in memory.
|
||||
* This isn't true for all calls, but it's safe to tell
|
||||
* gcc that it might happen so it doesn't get clever. */
|
||||
: "memory");
|
||||
return call;
|
||||
}
|
||||
/*:*/
|
||||
|
||||
void async_hcall(unsigned long call,
|
||||
unsigned long arg1, unsigned long arg2, unsigned long arg3);
|
||||
|
@ -52,31 +72,40 @@ struct hcall_ring
|
|||
u32 eax, edx, ebx, ecx;
|
||||
};
|
||||
|
||||
/* All the good stuff happens here: guest registers it with LGUEST_INIT */
|
||||
/*G:032 The second method of communicating with the Host is to via "struct
|
||||
* lguest_data". The Guest's very first hypercall is to tell the Host where
|
||||
* this is, and then the Guest and Host both publish information in it. :*/
|
||||
struct lguest_data
|
||||
{
|
||||
/* Fields which change during running: */
|
||||
/* 512 == enabled (same as eflags) */
|
||||
/* 512 == enabled (same as eflags in normal hardware). The Guest
|
||||
* changes interrupts so often that a hypercall is too slow. */
|
||||
unsigned int irq_enabled;
|
||||
/* Interrupts blocked by guest. */
|
||||
/* Fine-grained interrupt disabling by the Guest */
|
||||
DECLARE_BITMAP(blocked_interrupts, LGUEST_IRQS);
|
||||
|
||||
/* Virtual address of page fault. */
|
||||
/* The Host writes the virtual address of the last page fault here,
|
||||
* which saves the Guest a hypercall. CR2 is the native register where
|
||||
* this address would normally be found. */
|
||||
unsigned long cr2;
|
||||
|
||||
/* Async hypercall ring. 0xFF == done, 0 == pending. */
|
||||
/* Async hypercall ring. Instead of directly making hypercalls, we can
|
||||
* place them in here for processing the next time the Host wants.
|
||||
* This batching can be quite efficient. */
|
||||
|
||||
/* 0xFF == done (set by Host), 0 == pending (set by Guest). */
|
||||
u8 hcall_status[LHCALL_RING_SIZE];
|
||||
/* The actual registers for the hypercalls. */
|
||||
struct hcall_ring hcalls[LHCALL_RING_SIZE];
|
||||
|
||||
/* Fields initialized by the hypervisor at boot: */
|
||||
/* Fields initialized by the Host at boot: */
|
||||
/* Memory not to try to access */
|
||||
unsigned long reserve_mem;
|
||||
/* ID of this guest (used by network driver to set ethernet address) */
|
||||
/* ID of this Guest (used by network driver to set ethernet address) */
|
||||
u16 guestid;
|
||||
/* KHz for the TSC clock. */
|
||||
u32 tsc_khz;
|
||||
|
||||
/* Fields initialized by the guest at boot: */
|
||||
/* Fields initialized by the Guest at boot: */
|
||||
/* Instruction range to suppress interrupts even if enabled */
|
||||
unsigned long noirq_start, noirq_end;
|
||||
};
|
||||
|
|
Loading…
Reference in New Issue