[PATCH kernel v10 32/34] powerpc/mmu: Add userspace-to-physical addresses translation cache

[Alexey Kardashevskiy <aik@ozlabs.ru>]

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 a mapped pages counter; when it is zero, it is safe to
unregister the region.

Multiple registration of the same region is allowed, kref is used to
track the number of registrations. atomic_inc_not_zero() and
atomic_dec_if_positive() are used to decide whether to allow or deny
the mapped counter increments.

Each registered region keeps a counter for mapped TCEs plus one per
the registered area.

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>
---
Changes:
v10:
* split mm_iommu_mapped_update into mm_iommu_mapped_dec + mm_iommu_mapped_inc
* mapped counter now keep one reference for itself and mm_iommu_mapped_inc()
can tell if the region is being released
* updated commit log

v8:
* s/mm_iommu_table_group_mem_t/struct mm_iommu_table_group_mem_t/
* fixed error fallback look (s/[i]/[j]/)
---
 arch/powerpc/include/asm/mmu-hash64.h      |   3 +
 arch/powerpc/include/asm/mmu_context.h     |  17 +++
 arch/powerpc/mm/Makefile                   |   1 +
 arch/powerpc/mm/mmu_context_hash64.c       |   6 +
 arch/powerpc/mm/mmu_context_hash64_iommu.c | 221 +++++++++++++++++++++++++++++
 5 files changed, 248 insertions(+)
 create mode 100644 arch/powerpc/mm/mmu_context_hash64_iommu.c

diff --git a/arch/powerpc/include/asm/mmu-hash64.h b/arch/powerpc/include/asm/mmu-hash64.h
index 1da6a81..a82f534 100644
--- a/arch/powerpc/include/asm/mmu-hash64.h
+++ b/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;
 
 
diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 73382eb..138bb53 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -16,6 +16,23 @@
  */
 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_alloc(unsigned long ua, unsigned long entries,
+		struct mm_iommu_table_group_mem_t **pmem);
+extern struct mm_iommu_table_group_mem_t *mm_iommu_get(unsigned long ua,
+		unsigned long entries);
+extern long mm_iommu_put(struct mm_iommu_table_group_mem_t *mem);
+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 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 long 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);
diff --git a/arch/powerpc/mm/Makefile b/arch/powerpc/mm/Makefile
index 9c8770b..e216704 100644
--- a/arch/powerpc/mm/Makefile
+++ b/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_hash64_iommu.o
diff --git a/arch/powerpc/mm/mmu_context_hash64.c b/arch/powerpc/mm/mmu_context_hash64.c
index 178876ae..eb3080c 100644
--- a/arch/powerpc/mm/mmu_context_hash64.c
+++ b/arch/powerpc/mm/mmu_context_hash64.c
@@ -89,6 +89,9 @@ 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
+	INIT_LIST_HEAD_RCU(&mm->context.iommu_group_mem_list);
+#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);
diff --git a/arch/powerpc/mm/mmu_context_hash64_iommu.c b/arch/powerpc/mm/mmu_context_hash64_iommu.c
new file mode 100644
index 0000000..002c6c9
--- /dev/null
+++ b/arch/powerpc/mm/mmu_context_hash64_iommu.c
@@ -0,0 +1,221 @@
+/*
+ *  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/kref.h>
+#include <asm/mmu_context.h>
+
+struct mm_iommu_table_group_mem_t {
+	struct list_head next;
+	struct rcu_head rcu;
+	struct kref kref;	/* one reference per VFIO container */
+	atomic_t mapped;	/* number of currently mapped pages */
+	u64 ua;			/* userspace address */
+	u64 entries;		/* number of entries in hpas[] */
+	u64 *hpas;		/* vmalloc'ed */
+};
+
+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_alloc(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;
+	struct page *page = NULL;
+
+	list_for_each_entry_rcu(mem, &current->mm->context.iommu_group_mem_list,
+			next) {
+		if ((mem->ua == ua) && (mem->entries == entries))
+			return -EBUSY;
+
+		/* Overlap? */
+		if ((mem->ua < (ua + (entries << PAGE_SHIFT))) &&
+				(ua < (mem->ua + (mem->entries << PAGE_SHIFT))))
+			return -EINVAL;
+	}
+
+	mem = kzalloc(sizeof(*mem), GFP_KERNEL);
+	if (!mem)
+		return -ENOMEM;
+
+	mem->hpas = vzalloc(entries * sizeof(mem->hpas[0]));
+	if (!mem->hpas) {
+		kfree(mem);
+		return -ENOMEM;
+	}
+
+	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);
+			return -EFAULT;
+		}
+
+		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
+	}
+
+	kref_init(&mem->kref);
+	atomic_set(&mem->mapped, 1);
+	mem->ua = ua;
+	mem->entries = entries;
+	*pmem = mem;
+
+	list_add_rcu(&mem->next, &current->mm->context.iommu_group_mem_list);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(mm_iommu_alloc);
+
+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_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_unpin(mem);
+	vfree(mem->hpas);
+	kfree(mem);
+}
+
+static void mm_iommu_release(struct kref *kref)
+{
+	struct mm_iommu_table_group_mem_t *mem = container_of(kref,
+			struct mm_iommu_table_group_mem_t, kref);
+
+	list_del_rcu(&mem->next);
+	call_rcu(&mem->rcu, mm_iommu_free);
+}
+
+struct mm_iommu_table_group_mem_t *mm_iommu_get(unsigned long ua,
+		unsigned long entries)
+{
+	struct mm_iommu_table_group_mem_t *mem;
+
+	list_for_each_entry_rcu(mem, &current->mm->context.iommu_group_mem_list,
+			next) {
+		if ((mem->ua == ua) && (mem->entries == entries)) {
+			kref_get(&mem->kref);
+			return mem;
+		}
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(mm_iommu_get);
+
+long mm_iommu_put(struct mm_iommu_table_group_mem_t *mem)
+{
+	if (1 != atomic_dec_if_positive(&mem->mapped)) {
+		/* There are mappings, exit */
+		atomic_inc(&mem->mapped);
+		return -EBUSY;
+	}
+
+	kref_put(&mem->kref, mm_iommu_release);
+
+	return 0;
+}
+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);
+
+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 (atomic_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);
+
+long mm_iommu_mapped_dec(struct mm_iommu_table_group_mem_t *mem)
+{
+	return atomic_dec_if_positive(&mem->mapped);
+}
+EXPORT_SYMBOL_GPL(mm_iommu_mapped_dec);
+
+void mm_iommu_cleanup(mm_context_t *ctx)
+{
+	while (!list_empty(&ctx->iommu_group_mem_list)) {
+		struct mm_iommu_table_group_mem_t *mem;
+
+		mem = list_first_entry(&ctx->iommu_group_mem_list,
+				struct mm_iommu_table_group_mem_t, next);
+		mm_iommu_release(&mem->kref);
+	}
+}
-- 
2.4.0.rc3.8.gfb3e7d5