powerpc/mmu: Add userspace-to-physical addresses translation cache

We are adding support for DMA memory pre-registration to be used in
conjunction with VFIO. The idea is that the userspace which is going to
run a guest may want to pre-register a user space memory region so
it all gets pinned once and never goes away. Having this done,
a hypervisor will not have to pin/unpin pages on every DMA map/unmap
request. This is going to help with multiple pinning of the same memory.

Another use of it is in-kernel real mode (mmu off) acceleration of
DMA requests where real time translation of guest physical to host
physical addresses is non-trivial and may fail as linux ptes may be
temporarily invalid. Also, having cached host physical addresses
(compared to just pinning at the start and then walking the page table
again on every H_PUT_TCE), we can be sure that the addresses which we put
into TCE table are the ones we already pinned.

This adds a list of memory regions to mm_context_t. Each region consists
of a header and a list of physical addresses. This adds API to:
1. register/unregister memory regions;
2. do final cleanup (which puts all pre-registered pages);
3. do userspace to physical address translation;
4. manage usage counters; multiple registration of the same memory
is allowed (once per container).

This implements 2 counters per registered memory region:
- @mapped: incremented on every DMA mapping; decremented on unmapping;
initialized to 1 when a region is just registered; once it becomes zero,
no more mappings allowe;
- @used: incremented on every "register" ioctl; decremented on
"unregister"; unregistration is allowed for DMA mapped regions unless
it is the very last reference. For the very last reference this checks
that the region is still mapped and returns -EBUSY so the userspace
gets to know that memory is still pinned and unregistration needs to
be retried; @used remains 1.

Host physical addresses are stored in vmalloc'ed array. In order to
access these in the real mode (mmu off), there is a real_vmalloc_addr()
helper. In-kernel acceleration patchset will move it from KVM to MMU code.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/mmu-hash64.h

@@ -536,6 +536,9 @@ typedef struct {
 	/* for 4K PTE fragment support */
 	void *pte_frag;
 #endif
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+	struct list_head iommu_group_mem_list;
+#endif
 } mm_context_t;
 
 

arch/powerpc/include/asm/mmu_context.h

@@ -16,6 +16,24 @@
  */
 extern int init_new_context(struct task_struct *tsk, struct mm_struct *mm);
 extern void destroy_context(struct mm_struct *mm);
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+struct mm_iommu_table_group_mem_t;
+
+extern bool mm_iommu_preregistered(void);
+extern long mm_iommu_get(unsigned long ua, unsigned long entries,
+		struct mm_iommu_table_group_mem_t **pmem);
+extern long mm_iommu_put(struct mm_iommu_table_group_mem_t *mem);
+extern void mm_iommu_init(mm_context_t *ctx);
+extern void mm_iommu_cleanup(mm_context_t *ctx);
+extern struct mm_iommu_table_group_mem_t *mm_iommu_lookup(unsigned long ua,
+		unsigned long size);
+extern struct mm_iommu_table_group_mem_t *mm_iommu_find(unsigned long ua,
+		unsigned long entries);
+extern long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
+		unsigned long ua, unsigned long *hpa);
+extern long mm_iommu_mapped_inc(struct mm_iommu_table_group_mem_t *mem);
+extern void mm_iommu_mapped_dec(struct mm_iommu_table_group_mem_t *mem);
+#endif
 
 extern void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next);
 extern void switch_slb(struct task_struct *tsk, struct mm_struct *mm);

arch/powerpc/kernel/setup_64.c

@@ -686,6 +686,9 @@ void __init setup_arch(char **cmdline_p)
 	init_mm.brk = klimit;
 #ifdef CONFIG_PPC_64K_PAGES
 	init_mm.context.pte_frag = NULL;
+#endif
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+	mm_iommu_init(&init_mm.context);
 #endif
 	irqstack_early_init();
 	exc_lvl_early_init();

arch/powerpc/mm/Makefile

@@ -36,3 +36,4 @@ obj-$(CONFIG_PPC_SUBPAGE_PROT)	+= subpage-prot.o
 obj-$(CONFIG_NOT_COHERENT_CACHE) += dma-noncoherent.o
 obj-$(CONFIG_HIGHMEM)		+= highmem.o
 obj-$(CONFIG_PPC_COPRO_BASE)	+= copro_fault.o
+obj-$(CONFIG_SPAPR_TCE_IOMMU)	+= mmu_context_iommu.o

arch/powerpc/mm/mmu_context_hash64.c

@@ -88,6 +88,9 @@ int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 
 #ifdef CONFIG_PPC_64K_PAGES
 	mm->context.pte_frag = NULL;
+#endif
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+	mm_iommu_init(&mm->context);
 #endif
 	return 0;
 }
@@ -132,6 +135,9 @@ static inline void destroy_pagetable_page(struct mm_struct *mm)
 
 void destroy_context(struct mm_struct *mm)
 {
+#ifdef CONFIG_SPAPR_TCE_IOMMU
+	mm_iommu_cleanup(&mm->context);
+#endif
 
 #ifdef CONFIG_PPC_ICSWX
 	drop_cop(mm->context.acop, mm);

arch/powerpc/mm/mmu_context_iommu.c

@@ -0,0 +1,316 @@
+/*
+ *  IOMMU helpers in MMU context.
+ *
+ *  Copyright (C) 2015 IBM Corp. <aik@ozlabs.ru>
+ *
+ *  This program is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU General Public License
+ *  as published by the Free Software Foundation; either version
+ *  2 of the License, or (at your option) any later version.
+ *
+ */
+
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/rculist.h>
+#include <linux/vmalloc.h>
+#include <linux/mutex.h>
+#include <asm/mmu_context.h>
+
+static DEFINE_MUTEX(mem_list_mutex);
+
+struct mm_iommu_table_group_mem_t {
+	struct list_head next;
+	struct rcu_head rcu;
+	unsigned long used;
+	atomic64_t mapped;
+	u64 ua;			/* userspace address */
+	u64 entries;		/* number of entries in hpas[] */
+	u64 *hpas;		/* vmalloc'ed */
+};
+
+static long mm_iommu_adjust_locked_vm(struct mm_struct *mm,
+		unsigned long npages, bool incr)
+{
+	long ret = 0, locked, lock_limit;
+
+	if (!npages)
+		return 0;
+
+	down_write(&mm->mmap_sem);
+
+	if (incr) {
+		locked = mm->locked_vm + npages;
+		lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
+			ret = -ENOMEM;
+		else
+			mm->locked_vm += npages;
+	} else {
+		if (WARN_ON_ONCE(npages > mm->locked_vm))
+			npages = mm->locked_vm;
+		mm->locked_vm -= npages;
+	}
+
+	pr_debug("[%d] RLIMIT_MEMLOCK HASH64 %c%ld %ld/%ld\n",
+			current->pid,
+			incr ? '+' : '-',
+			npages << PAGE_SHIFT,
+			mm->locked_vm << PAGE_SHIFT,
+			rlimit(RLIMIT_MEMLOCK));
+	up_write(&mm->mmap_sem);
+
+	return ret;
+}
+
+bool mm_iommu_preregistered(void)
+{
+	if (!current || !current->mm)
+		return false;
+
+	return !list_empty(&current->mm->context.iommu_group_mem_list);
+}
+EXPORT_SYMBOL_GPL(mm_iommu_preregistered);
+
+long mm_iommu_get(unsigned long ua, unsigned long entries,
+		struct mm_iommu_table_group_mem_t **pmem)
+{
+	struct mm_iommu_table_group_mem_t *mem;
+	long i, j, ret = 0, locked_entries = 0;
+	struct page *page = NULL;
+
+	if (!current || !current->mm)
+		return -ESRCH; /* process exited */
+
+	mutex_lock(&mem_list_mutex);
+
+	list_for_each_entry_rcu(mem, &current->mm->context.iommu_group_mem_list,
+			next) {
+		if ((mem->ua == ua) && (mem->entries == entries)) {
+			++mem->used;
+			*pmem = mem;
+			goto unlock_exit;
+		}
+
+		/* Overlap? */
+		if ((mem->ua < (ua + (entries << PAGE_SHIFT))) &&
+				(ua < (mem->ua +
+				       (mem->entries << PAGE_SHIFT)))) {
+			ret = -EINVAL;
+			goto unlock_exit;
+		}
+
+	}
+
+	ret = mm_iommu_adjust_locked_vm(current->mm, entries, true);
+	if (ret)
+		goto unlock_exit;
+
+	locked_entries = entries;
+
+	mem = kzalloc(sizeof(*mem), GFP_KERNEL);
+	if (!mem) {
+		ret = -ENOMEM;
+		goto unlock_exit;
+	}
+
+	mem->hpas = vzalloc(entries * sizeof(mem->hpas[0]));
+	if (!mem->hpas) {
+		kfree(mem);
+		ret = -ENOMEM;
+		goto unlock_exit;
+	}
+
+	for (i = 0; i < entries; ++i) {
+		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
+					1/* pages */, 1/* iswrite */, &page)) {
+			for (j = 0; j < i; ++j)
+				put_page(pfn_to_page(
+						mem->hpas[j] >> PAGE_SHIFT));
+			vfree(mem->hpas);
+			kfree(mem);
+			ret = -EFAULT;
+			goto unlock_exit;
+		}
+
+		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
+	}
+
+	atomic64_set(&mem->mapped, 1);
+	mem->used = 1;
+	mem->ua = ua;
+	mem->entries = entries;
+	*pmem = mem;
+
+	list_add_rcu(&mem->next, &current->mm->context.iommu_group_mem_list);
+
+unlock_exit:
+	if (locked_entries && ret)
+		mm_iommu_adjust_locked_vm(current->mm, locked_entries, false);
+
+	mutex_unlock(&mem_list_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(mm_iommu_get);
+
+static void mm_iommu_unpin(struct mm_iommu_table_group_mem_t *mem)
+{
+	long i;
+	struct page *page = NULL;
+
+	for (i = 0; i < mem->entries; ++i) {
+		if (!mem->hpas[i])
+			continue;
+
+		page = pfn_to_page(mem->hpas[i] >> PAGE_SHIFT);
+		if (!page)
+			continue;
+
+		put_page(page);
+		mem->hpas[i] = 0;
+	}
+}
+
+static void mm_iommu_do_free(struct mm_iommu_table_group_mem_t *mem)
+{
+
+	mm_iommu_unpin(mem);
+	vfree(mem->hpas);
+	kfree(mem);
+}
+
+static void mm_iommu_free(struct rcu_head *head)
+{
+	struct mm_iommu_table_group_mem_t *mem = container_of(head,
+			struct mm_iommu_table_group_mem_t, rcu);
+
+	mm_iommu_do_free(mem);
+}
+
+static void mm_iommu_release(struct mm_iommu_table_group_mem_t *mem)
+{
+	list_del_rcu(&mem->next);
+	mm_iommu_adjust_locked_vm(current->mm, mem->entries, false);
+	call_rcu(&mem->rcu, mm_iommu_free);
+}
+
+long mm_iommu_put(struct mm_iommu_table_group_mem_t *mem)
+{
+	long ret = 0;
+
+	if (!current || !current->mm)
+		return -ESRCH; /* process exited */
+
+	mutex_lock(&mem_list_mutex);
+
+	if (mem->used == 0) {
+		ret = -ENOENT;
+		goto unlock_exit;
+	}
+
+	--mem->used;
+	/* There are still users, exit */
+	if (mem->used)
+		goto unlock_exit;
+
+	/* Are there still mappings? */
+	if (atomic_cmpxchg(&mem->mapped, 1, 0) != 1) {
+		++mem->used;
+		ret = -EBUSY;
+		goto unlock_exit;
+	}
+
+	/* @mapped became 0 so now mappings are disabled, release the region */
+	mm_iommu_release(mem);
+
+unlock_exit:
+	mutex_unlock(&mem_list_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(mm_iommu_put);
+
+struct mm_iommu_table_group_mem_t *mm_iommu_lookup(unsigned long ua,
+		unsigned long size)
+{
+	struct mm_iommu_table_group_mem_t *mem, *ret = NULL;
+
+	list_for_each_entry_rcu(mem,
+			&current->mm->context.iommu_group_mem_list,
+			next) {
+		if ((mem->ua <= ua) &&
+				(ua + size <= mem->ua +
+				 (mem->entries << PAGE_SHIFT))) {
+			ret = mem;
+			break;
+		}
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(mm_iommu_lookup);
+
+struct mm_iommu_table_group_mem_t *mm_iommu_find(unsigned long ua,
+		unsigned long entries)
+{
+	struct mm_iommu_table_group_mem_t *mem, *ret = NULL;
+
+	list_for_each_entry_rcu(mem,
+			&current->mm->context.iommu_group_mem_list,
+			next) {
+		if ((mem->ua == ua) && (mem->entries == entries)) {
+			ret = mem;
+			break;
+		}
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(mm_iommu_find);
+
+long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
+		unsigned long ua, unsigned long *hpa)
+{
+	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
+	u64 *va = &mem->hpas[entry];
+
+	if (entry >= mem->entries)
+		return -EFAULT;
+
+	*hpa = *va | (ua & ~PAGE_MASK);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(mm_iommu_ua_to_hpa);
+
+long mm_iommu_mapped_inc(struct mm_iommu_table_group_mem_t *mem)
+{
+	if (atomic64_inc_not_zero(&mem->mapped))
+		return 0;
+
+	/* Last mm_iommu_put() has been called, no more mappings allowed() */
+	return -ENXIO;
+}
+EXPORT_SYMBOL_GPL(mm_iommu_mapped_inc);
+
+void mm_iommu_mapped_dec(struct mm_iommu_table_group_mem_t *mem)
+{
+	atomic64_add_unless(&mem->mapped, -1, 1);
+}
+EXPORT_SYMBOL_GPL(mm_iommu_mapped_dec);
+
+void mm_iommu_init(mm_context_t *ctx)
+{
+	INIT_LIST_HEAD_RCU(&ctx->iommu_group_mem_list);
+}
+
+void mm_iommu_cleanup(mm_context_t *ctx)
+{
+	struct mm_iommu_table_group_mem_t *mem, *tmp;
+
+	list_for_each_entry_safe(mem, tmp, &ctx->iommu_group_mem_list, next) {
+		list_del_rcu(&mem->next);
+		mm_iommu_do_free(mem);
+	}
+}