370 lines
10 KiB
C
370 lines
10 KiB
C
/*P:400
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* This contains run_guest() which actually calls into the Host<->Guest
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* Switcher and analyzes the return, such as determining if the Guest wants the
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* Host to do something. This file also contains useful helper routines.
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:*/
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#include <linux/module.h>
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#include <linux/stringify.h>
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#include <linux/stddef.h>
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#include <linux/io.h>
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#include <linux/mm.h>
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#include <linux/vmalloc.h>
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#include <linux/cpu.h>
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#include <linux/freezer.h>
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#include <linux/highmem.h>
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#include <linux/slab.h>
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#include <asm/paravirt.h>
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#include <asm/pgtable.h>
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#include <asm/uaccess.h>
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#include <asm/poll.h>
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#include <asm/asm-offsets.h>
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#include "lg.h"
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unsigned long switcher_addr;
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struct page **lg_switcher_pages;
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static struct vm_struct *switcher_vma;
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/* This One Big lock protects all inter-guest data structures. */
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DEFINE_MUTEX(lguest_lock);
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/*H:010
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* We need to set up the Switcher at a high virtual address. Remember the
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* Switcher is a few hundred bytes of assembler code which actually changes the
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* CPU to run the Guest, and then changes back to the Host when a trap or
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* interrupt happens.
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*
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* The Switcher code must be at the same virtual address in the Guest as the
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* Host since it will be running as the switchover occurs.
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*
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* Trying to map memory at a particular address is an unusual thing to do, so
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* it's not a simple one-liner.
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*/
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static __init int map_switcher(void)
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{
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int i, err;
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/*
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* Map the Switcher in to high memory.
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*
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* It turns out that if we choose the address 0xFFC00000 (4MB under the
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* top virtual address), it makes setting up the page tables really
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* easy.
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*/
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/* We assume Switcher text fits into a single page. */
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if (end_switcher_text - start_switcher_text > PAGE_SIZE) {
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printk(KERN_ERR "lguest: switcher text too large (%zu)\n",
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end_switcher_text - start_switcher_text);
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return -EINVAL;
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}
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/*
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* We allocate an array of struct page pointers. map_vm_area() wants
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* this, rather than just an array of pages.
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*/
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lg_switcher_pages = kmalloc(sizeof(lg_switcher_pages[0])
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* TOTAL_SWITCHER_PAGES,
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GFP_KERNEL);
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if (!lg_switcher_pages) {
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err = -ENOMEM;
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goto out;
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}
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/*
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* Now we actually allocate the pages. The Guest will see these pages,
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* so we make sure they're zeroed.
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*/
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for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
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lg_switcher_pages[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
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if (!lg_switcher_pages[i]) {
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err = -ENOMEM;
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goto free_some_pages;
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}
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}
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/*
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* We place the Switcher underneath the fixmap area, which is the
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* highest virtual address we can get. This is important, since we
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* tell the Guest it can't access this memory, so we want its ceiling
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* as high as possible.
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*/
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switcher_addr = FIXADDR_START - (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE;
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/*
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* Now we reserve the "virtual memory area" we want. We might
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* not get it in theory, but in practice it's worked so far.
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* The end address needs +1 because __get_vm_area allocates an
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* extra guard page, so we need space for that.
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*/
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switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
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VM_ALLOC, switcher_addr, switcher_addr
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+ (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
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if (!switcher_vma) {
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err = -ENOMEM;
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printk("lguest: could not map switcher pages high\n");
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goto free_pages;
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}
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/*
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* This code actually sets up the pages we've allocated to appear at
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* switcher_addr. map_vm_area() takes the vma we allocated above, the
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* kind of pages we're mapping (kernel pages), and a pointer to our
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* array of struct pages.
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*/
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err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, lg_switcher_pages);
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if (err) {
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printk("lguest: map_vm_area failed: %i\n", err);
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goto free_vma;
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}
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/*
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* Now the Switcher is mapped at the right address, we can't fail!
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* Copy in the compiled-in Switcher code (from x86/switcher_32.S).
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*/
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memcpy(switcher_vma->addr, start_switcher_text,
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end_switcher_text - start_switcher_text);
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printk(KERN_INFO "lguest: mapped switcher at %p\n",
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switcher_vma->addr);
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/* And we succeeded... */
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return 0;
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free_vma:
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vunmap(switcher_vma->addr);
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free_pages:
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i = TOTAL_SWITCHER_PAGES;
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free_some_pages:
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for (--i; i >= 0; i--)
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__free_pages(lg_switcher_pages[i], 0);
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kfree(lg_switcher_pages);
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out:
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return err;
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}
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/*:*/
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/* Cleaning up the mapping when the module is unloaded is almost... too easy. */
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static void unmap_switcher(void)
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{
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unsigned int i;
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/* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
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vunmap(switcher_vma->addr);
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/* Now we just need to free the pages we copied the switcher into */
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for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
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__free_pages(lg_switcher_pages[i], 0);
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kfree(lg_switcher_pages);
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}
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/*H:032
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* Dealing With Guest Memory.
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*
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* Before we go too much further into the Host, we need to grok the routines
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* we use to deal with Guest memory.
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*
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* When the Guest gives us (what it thinks is) a physical address, we can use
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* the normal copy_from_user() & copy_to_user() on the corresponding place in
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* the memory region allocated by the Launcher.
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*
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* But we can't trust the Guest: it might be trying to access the Launcher
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* code. We have to check that the range is below the pfn_limit the Launcher
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* gave us. We have to make sure that addr + len doesn't give us a false
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* positive by overflowing, too.
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*/
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bool lguest_address_ok(const struct lguest *lg,
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unsigned long addr, unsigned long len)
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{
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return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
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}
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/*
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* This routine copies memory from the Guest. Here we can see how useful the
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* kill_lguest() routine we met in the Launcher can be: we return a random
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* value (all zeroes) instead of needing to return an error.
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*/
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void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
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{
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if (!lguest_address_ok(cpu->lg, addr, bytes)
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|| copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
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/* copy_from_user should do this, but as we rely on it... */
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memset(b, 0, bytes);
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kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
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}
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}
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/* This is the write (copy into Guest) version. */
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void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
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unsigned bytes)
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{
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if (!lguest_address_ok(cpu->lg, addr, bytes)
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|| copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
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kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
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}
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/*:*/
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/*H:030
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* Let's jump straight to the the main loop which runs the Guest.
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* Remember, this is called by the Launcher reading /dev/lguest, and we keep
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* going around and around until something interesting happens.
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*/
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int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
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{
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/* If the launcher asked for a register with LHREQ_GETREG */
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if (cpu->reg_read) {
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if (put_user(*cpu->reg_read, user))
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return -EFAULT;
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cpu->reg_read = NULL;
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return sizeof(*cpu->reg_read);
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}
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/* We stop running once the Guest is dead. */
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while (!cpu->lg->dead) {
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unsigned int irq;
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bool more;
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/* First we run any hypercalls the Guest wants done. */
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if (cpu->hcall)
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do_hypercalls(cpu);
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/* Do we have to tell the Launcher about a trap? */
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if (cpu->pending.trap) {
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if (copy_to_user(user, &cpu->pending,
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sizeof(cpu->pending)))
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return -EFAULT;
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return sizeof(cpu->pending);
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}
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/*
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* All long-lived kernel loops need to check with this horrible
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* thing called the freezer. If the Host is trying to suspend,
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* it stops us.
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*/
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try_to_freeze();
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/* Check for signals */
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if (signal_pending(current))
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return -ERESTARTSYS;
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/*
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* Check if there are any interrupts which can be delivered now:
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* if so, this sets up the hander to be executed when we next
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* run the Guest.
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*/
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irq = interrupt_pending(cpu, &more);
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if (irq < LGUEST_IRQS)
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try_deliver_interrupt(cpu, irq, more);
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/*
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* Just make absolutely sure the Guest is still alive. One of
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* those hypercalls could have been fatal, for example.
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*/
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if (cpu->lg->dead)
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break;
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/*
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* If the Guest asked to be stopped, we sleep. The Guest's
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* clock timer will wake us.
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*/
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if (cpu->halted) {
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set_current_state(TASK_INTERRUPTIBLE);
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/*
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* Just before we sleep, make sure no interrupt snuck in
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* which we should be doing.
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*/
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if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
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set_current_state(TASK_RUNNING);
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else
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schedule();
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continue;
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}
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/*
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* OK, now we're ready to jump into the Guest. First we put up
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* the "Do Not Disturb" sign:
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*/
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local_irq_disable();
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/* Actually run the Guest until something happens. */
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lguest_arch_run_guest(cpu);
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/* Now we're ready to be interrupted or moved to other CPUs */
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local_irq_enable();
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/* Now we deal with whatever happened to the Guest. */
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lguest_arch_handle_trap(cpu);
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}
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/* Special case: Guest is 'dead' but wants a reboot. */
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if (cpu->lg->dead == ERR_PTR(-ERESTART))
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return -ERESTART;
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/* The Guest is dead => "No such file or directory" */
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return -ENOENT;
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}
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/*H:000
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* Welcome to the Host!
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*
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* By this point your brain has been tickled by the Guest code and numbed by
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* the Launcher code; prepare for it to be stretched by the Host code. This is
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* the heart. Let's begin at the initialization routine for the Host's lg
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* module.
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*/
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static int __init init(void)
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{
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int err;
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/* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */
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if (get_kernel_rpl() != 0) {
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printk("lguest is afraid of being a guest\n");
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return -EPERM;
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}
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/* First we put the Switcher up in very high virtual memory. */
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err = map_switcher();
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if (err)
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goto out;
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/* We might need to reserve an interrupt vector. */
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err = init_interrupts();
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if (err)
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goto unmap;
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/* /dev/lguest needs to be registered. */
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err = lguest_device_init();
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if (err)
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goto free_interrupts;
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/* Finally we do some architecture-specific setup. */
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lguest_arch_host_init();
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/* All good! */
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return 0;
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free_interrupts:
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free_interrupts();
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unmap:
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unmap_switcher();
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out:
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return err;
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}
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/* Cleaning up is just the same code, backwards. With a little French. */
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static void __exit fini(void)
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{
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lguest_device_remove();
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free_interrupts();
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unmap_switcher();
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lguest_arch_host_fini();
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}
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/*:*/
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/*
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* The Host side of lguest can be a module. This is a nice way for people to
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* play with it.
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*/
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module_init(init);
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module_exit(fini);
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
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