[PATCH] KVM: MMU: Shadow page table caching

Define a hashtable for caching shadow page tables. Look up the cache on
context switch (cr3 change) or during page faults.

The key to the cache is a combination of
- the guest page table frame number
- the number of paging levels in the guest
   * we can cache real mode, 32-bit mode, pae, and long mode page
     tables simultaneously.  this is useful for smp bootup.
- the guest page table table
   * some kernels use a page as both a page table and a page directory.  this
     allows multiple shadow pages to exist for that page, one per level
- the "quadrant"
   * 32-bit mode page tables span 4MB, whereas a shadow page table spans
     2MB.  similarly, a 32-bit page directory spans 4GB, while a shadow
     page directory spans 1GB.  the quadrant allows caching up to 4 shadow page
     tables for one guest page in one level.
- a "metaphysical" bit
   * for real mode, and for pse pages, there is no guest page table, so set
     the bit to avoid write protecting the page.

Signed-off-by: Avi Kivity <avi@qumranet.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 183 insertions, 24 deletions

diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index da4d7ddb9bdc..47c699c21c08 100644
--- a/drivers/kvm/mmu.c
+++ b/drivers/kvm/mmu.c
@@ -26,8 +26,8 @@
 #include "vmx.h"
 #include "kvm.h"
 
-#define pgprintk(x...) do { } while (0)
-#define rmap_printk(x...) do { } while (0)
+#define pgprintk(x...) do { printk(x); } while (0)
+#define rmap_printk(x...) do { printk(x); } while (0)
 
 #define ASSERT(x)                                                       \
         if (!(x)) {                                                     \
@@ -35,8 +35,10 @@
                        __FILE__, __LINE__, #x);                         \
         }
 
-#define PT64_ENT_PER_PAGE 512
-#define PT32_ENT_PER_PAGE 1024
+#define PT64_PT_BITS 9
+#define PT64_ENT_PER_PAGE (1 << PT64_PT_BITS)
+#define PT32_PT_BITS 10
+#define PT32_ENT_PER_PAGE (1 << PT32_PT_BITS)
 
 #define PT_WRITABLE_SHIFT 1
 
@@ -292,6 +294,11 @@ static int is_empty_shadow_page(hpa_t page_hpa)
         return 1;
 }
 
+static unsigned kvm_page_table_hashfn(gfn_t gfn)
+{
+        return gfn;
+}
+
 static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
                                                u64 *parent_pte)
 {
@@ -306,10 +313,147 @@ static struct kvm_mmu_page *kvm_mmu_alloc_page(struct kvm_vcpu *vcpu,
         ASSERT(is_empty_shadow_page(page->page_hpa));
         page->slot_bitmap = 0;
         page->global = 1;
+        page->multimapped = 0;
         page->parent_pte = parent_pte;
         return page;
 }
 
+static void mmu_page_add_parent_pte(struct kvm_mmu_page *page, u64 *parent_pte)
+{
+        struct kvm_pte_chain *pte_chain;
+        struct hlist_node *node;
+        int i;
+
+        if (!parent_pte)
+                return;
+        if (!page->multimapped) {
+                u64 *old = page->parent_pte;
+
+                if (!old) {
+                        page->parent_pte = parent_pte;
+                        return;
+                }
+                page->multimapped = 1;
+                pte_chain = kzalloc(sizeof(struct kvm_pte_chain), GFP_NOWAIT);
+                BUG_ON(!pte_chain);
+                INIT_HLIST_HEAD(&page->parent_ptes);
+                hlist_add_head(&pte_chain->link, &page->parent_ptes);
+                pte_chain->parent_ptes[0] = old;
+        }
+        hlist_for_each_entry(pte_chain, node, &page->parent_ptes, link) {
+                if (pte_chain->parent_ptes[NR_PTE_CHAIN_ENTRIES-1])
+                        continue;
+                for (i = 0; i < NR_PTE_CHAIN_ENTRIES; ++i)
+                        if (!pte_chain->parent_ptes[i]) {
+                                pte_chain->parent_ptes[i] = parent_pte;
+                                return;
+                        }
+        }
+        pte_chain = kzalloc(sizeof(struct kvm_pte_chain), GFP_NOWAIT);
+        BUG_ON(!pte_chain);
+        hlist_add_head(&pte_chain->link, &page->parent_ptes);
+        pte_chain->parent_ptes[0] = parent_pte;
+}
+
+static void mmu_page_remove_parent_pte(struct kvm_mmu_page *page,
+                                       u64 *parent_pte)
+{
+        struct kvm_pte_chain *pte_chain;
+        struct hlist_node *node;
+        int i;
+
+        if (!page->multimapped) {
+                BUG_ON(page->parent_pte != parent_pte);
+                page->parent_pte = NULL;
+                return;
+        }
+        hlist_for_each_entry(pte_chain, node, &page->parent_ptes, link)
+                for (i = 0; i < NR_PTE_CHAIN_ENTRIES; ++i) {
+                        if (!pte_chain->parent_ptes[i])
+                                break;
+                        if (pte_chain->parent_ptes[i] != parent_pte)
+                                continue;
+                        while (i + 1 < NR_PTE_CHAIN_ENTRIES) {
+                                pte_chain->parent_ptes[i]
+                                        = pte_chain->parent_ptes[i + 1];
+                                ++i;
+                        }
+                        pte_chain->parent_ptes[i] = NULL;
+                        return;
+                }
+        BUG();
+}
+
+static struct kvm_mmu_page *kvm_mmu_lookup_page(struct kvm_vcpu *vcpu,
+                                                gfn_t gfn)
+{
+        unsigned index;
+        struct hlist_head *bucket;
+        struct kvm_mmu_page *page;
+        struct hlist_node *node;
+
+        pgprintk("%s: looking for gfn %lx\n", __FUNCTION__, gfn);
+        index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
+        bucket = &vcpu->kvm->mmu_page_hash[index];
+        hlist_for_each_entry(page, node, bucket, hash_link)
+                if (page->gfn == gfn && !page->role.metaphysical) {
+                        pgprintk("%s: found role %x\n",
+                                 __FUNCTION__, page->role.word);
+                        return page;
+                }
+        return NULL;
+}
+
+static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
+                                             gfn_t gfn,
+                                             gva_t gaddr,
+                                             unsigned level,
+                                             int metaphysical,
+                                             u64 *parent_pte)
+{
+        union kvm_mmu_page_role role;
+        unsigned index;
+        unsigned quadrant;
+        struct hlist_head *bucket;
+        struct kvm_mmu_page *page;
+        struct hlist_node *node;
+
+        role.word = 0;
+        role.glevels = vcpu->mmu.root_level;
+        role.level = level;
+        role.metaphysical = metaphysical;
+        if (vcpu->mmu.root_level <= PT32_ROOT_LEVEL) {
+                quadrant = gaddr >> (PAGE_SHIFT + (PT64_PT_BITS * level));
+                quadrant &= (1 << ((PT32_PT_BITS - PT64_PT_BITS) * level)) - 1;
+                role.quadrant = quadrant;
+        }
+        pgprintk("%s: looking gfn %lx role %x\n", __FUNCTION__,
+                 gfn, role.word);
+        index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
+        bucket = &vcpu->kvm->mmu_page_hash[index];
+        hlist_for_each_entry(page, node, bucket, hash_link)
+                if (page->gfn == gfn && page->role.word == role.word) {
+                        mmu_page_add_parent_pte(page, parent_pte);
+                        pgprintk("%s: found\n", __FUNCTION__);
+                        return page;
+                }
+        page = kvm_mmu_alloc_page(vcpu, parent_pte);
+        if (!page)
+                return page;
+        pgprintk("%s: adding gfn %lx role %x\n", __FUNCTION__, gfn, role.word);
+        page->gfn = gfn;
+        page->role = role;
+        hlist_add_head(&page->hash_link, bucket);
+        return page;
+}
+
+static void kvm_mmu_put_page(struct kvm_vcpu *vcpu,
+                             struct kvm_mmu_page *page,
+                             u64 *parent_pte)
+{
+        mmu_page_remove_parent_pte(page, parent_pte);
+}
+
 static void page_header_update_slot(struct kvm *kvm, void *pte, gpa_t gpa)
 {
         int slot = memslot_id(kvm, gfn_to_memslot(kvm, gpa >> PAGE_SHIFT));
@@ -389,11 +533,15 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, hpa_t p)
         for (; ; level--) {
                 u32 index = PT64_INDEX(v, level);
                 u64 *table;
+                u64 pte;
 
                 ASSERT(VALID_PAGE(table_addr));
                 table = __va(table_addr);
 
                 if (level == 1) {
+                        pte = table[index];
+                        if (is_present_pte(pte) && is_writeble_pte(pte))
+                                return 0;
                         mark_page_dirty(vcpu->kvm, v >> PAGE_SHIFT);
                         page_header_update_slot(vcpu->kvm, table, v);
                         table[index] = p | PT_PRESENT_MASK | PT_WRITABLE_MASK |
@@ -404,8 +552,13 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, hpa_t p)
 
                 if (table[index] == 0) {
                         struct kvm_mmu_page *new_table;
+                        gfn_t pseudo_gfn;
 
-                        new_table = kvm_mmu_alloc_page(vcpu, &table[index]);
+                        pseudo_gfn = (v & PT64_DIR_BASE_ADDR_MASK)
+                                >> PAGE_SHIFT;
+                        new_table = kvm_mmu_get_page(vcpu, pseudo_gfn,
+                                                     v, level - 1,
+                                                     1, &table[index]);
                         if (!new_table) {
                                 pgprintk("nonpaging_map: ENOMEM\n");
                                 return -ENOMEM;
@@ -427,7 +580,6 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
                 hpa_t root = vcpu->mmu.root_hpa;
 
                 ASSERT(VALID_PAGE(root));
-                release_pt_page_64(vcpu, root, PT64_ROOT_LEVEL);
                 vcpu->mmu.root_hpa = INVALID_PAGE;
                 return;
         }
@@ -437,7 +589,6 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
 
                 ASSERT(VALID_PAGE(root));
                 root &= PT64_BASE_ADDR_MASK;
-                release_pt_page_64(vcpu, root, PT32E_ROOT_LEVEL - 1);
                 vcpu->mmu.pae_root[i] = INVALID_PAGE;
         }
         vcpu->mmu.root_hpa = INVALID_PAGE;
@@ -446,13 +597,16 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
 static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
 {
         int i;
+        gfn_t root_gfn;
+        root_gfn = vcpu->cr3 >> PAGE_SHIFT;
 
 #ifdef CONFIG_X86_64
         if (vcpu->mmu.shadow_root_level == PT64_ROOT_LEVEL) {
                 hpa_t root = vcpu->mmu.root_hpa;
 
                 ASSERT(!VALID_PAGE(root));
-                root = kvm_mmu_alloc_page(vcpu, NULL)->page_hpa;
+                root = kvm_mmu_get_page(vcpu, root_gfn, 0,
+                                        PT64_ROOT_LEVEL, 0, NULL)->page_hpa;
                 vcpu->mmu.root_hpa = root;
                 return;
         }
@@ -461,7 +615,13 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
                 hpa_t root = vcpu->mmu.pae_root[i];
 
                 ASSERT(!VALID_PAGE(root));
-                root = kvm_mmu_alloc_page(vcpu, NULL)->page_hpa;
+                if (vcpu->mmu.root_level == PT32E_ROOT_LEVEL)
+                        root_gfn = vcpu->pdptrs[i] >> PAGE_SHIFT;
+                else if (vcpu->mmu.root_level == 0)
+                        root_gfn = 0;
+                root = kvm_mmu_get_page(vcpu, root_gfn, i << 30,
+                                        PT32_ROOT_LEVEL, !is_paging(vcpu),
+                                        NULL)->page_hpa;
                 vcpu->mmu.pae_root[i] = root | PT_PRESENT_MASK;
         }
         vcpu->mmu.root_hpa = __pa(vcpu->mmu.pae_root);
@@ -529,7 +689,7 @@ static int nonpaging_init_context(struct kvm_vcpu *vcpu)
         context->inval_page = nonpaging_inval_page;
         context->gva_to_gpa = nonpaging_gva_to_gpa;
         context->free = nonpaging_free;
-        context->root_level = PT32E_ROOT_LEVEL;
+        context->root_level = 0;
         context->shadow_root_level = PT32E_ROOT_LEVEL;
         mmu_alloc_roots(vcpu);
         ASSERT(VALID_PAGE(context->root_hpa));
@@ -537,29 +697,18 @@ static int nonpaging_init_context(struct kvm_vcpu *vcpu)
         return 0;
 }
 
-
 static void kvm_mmu_flush_tlb(struct kvm_vcpu *vcpu)
 {
-        struct kvm_mmu_page *page, *npage;
-
-        list_for_each_entry_safe(page, npage, &vcpu->kvm->active_mmu_pages,
-                                 link) {
-                if (page->global)
-                        continue;
-
-                if (!page->parent_pte)
-                        continue;
-
-                *page->parent_pte = 0;
-                release_pt_page_64(vcpu, page->page_hpa, 1);
-        }
         ++kvm_stat.tlb_flush;
         kvm_arch_ops->tlb_flush(vcpu);
 }
 
 static void paging_new_cr3(struct kvm_vcpu *vcpu)
 {
+        mmu_free_roots(vcpu);
+        mmu_alloc_roots(vcpu);
         kvm_mmu_flush_tlb(vcpu);
+        kvm_arch_ops->set_cr3(vcpu, vcpu->mmu.root_hpa);
 }
 
 static void mark_pagetable_nonglobal(void *shadow_pte)
@@ -578,6 +727,16 @@ static inline void set_pte_common(struct kvm_vcpu *vcpu,
         *shadow_pte |= access_bits << PT_SHADOW_BITS_OFFSET;
         if (!dirty)
                 access_bits &= ~PT_WRITABLE_MASK;
+        if (access_bits & PT_WRITABLE_MASK) {
+                struct kvm_mmu_page *shadow;
+
+                shadow = kvm_mmu_lookup_page(vcpu, gaddr >> PAGE_SHIFT);
+                if (shadow)
+                        pgprintk("%s: found shadow page for %lx, marking ro\n",
+                                 __FUNCTION__, (gfn_t)(gaddr >> PAGE_SHIFT));
+                if (shadow)
+                        access_bits &= ~PT_WRITABLE_MASK;
+        }
 
         if (access_bits & PT_WRITABLE_MASK)
                 mark_page_dirty(vcpu->kvm, gaddr >> PAGE_SHIFT);