Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=cea0f0e7ea54753c3265dc77f605a6dad1912cfc
Commit:     cea0f0e7ea54753c3265dc77f605a6dad1912cfc
Parent:     25c0de2cc6c26cb99553c2444936a7951c120c09
Author:     Avi Kivity <[EMAIL PROTECTED]>
AuthorDate: Fri Jan 5 16:36:43 2007 -0800
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Fri Jan 5 23:55:24 2007 -0800

    [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 <[EMAIL PROTECTED]>
    Acked-by: Ingo Molnar <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 drivers/kvm/kvm.h         |   45 ++++++++++-
 drivers/kvm/mmu.c         |  207 +++++++++++++++++++++++++++++++++++++++-----
 drivers/kvm/paging_tmpl.h |   62 ++++++++++++--
 3 files changed, 280 insertions(+), 34 deletions(-)

diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index abe40dd..58b9deb 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -89,14 +89,53 @@ typedef unsigned long  hva_t;
 typedef u64            hpa_t;
 typedef unsigned long  hfn_t;
 
+#define NR_PTE_CHAIN_ENTRIES 5
+
+struct kvm_pte_chain {
+       u64 *parent_ptes[NR_PTE_CHAIN_ENTRIES];
+       struct hlist_node link;
+};
+
+/*
+ * kvm_mmu_page_role, below, is defined as:
+ *
+ *   bits 0:3 - total guest paging levels (2-4, or zero for real mode)
+ *   bits 4:7 - page table level for this shadow (1-4)
+ *   bits 8:9 - page table quadrant for 2-level guests
+ *   bit   16 - "metaphysical" - gfn is not a real page (huge page/real mode)
+ */
+union kvm_mmu_page_role {
+       unsigned word;
+       struct {
+               unsigned glevels : 4;
+               unsigned level : 4;
+               unsigned quadrant : 2;
+               unsigned pad_for_nice_hex_output : 6;
+               unsigned metaphysical : 1;
+       };
+};
+
 struct kvm_mmu_page {
        struct list_head link;
+       struct hlist_node hash_link;
+
+       /*
+        * The following two entries are used to key the shadow page in the
+        * hash table.
+        */
+       gfn_t gfn;
+       union kvm_mmu_page_role role;
+
        hpa_t page_hpa;
        unsigned long slot_bitmap; /* One bit set per slot which has memory
                                    * in this shadow page.
                                    */
        int global;              /* Set if all ptes in this page are global */
-       u64 *parent_pte;
+       int multimapped;         /* More than one parent_pte? */
+       union {
+               u64 *parent_pte;               /* !multimapped */
+               struct hlist_head parent_ptes; /* multimapped, kvm_pte_chain */
+       };
 };
 
 struct vmcs {
@@ -235,7 +274,11 @@ struct kvm {
        spinlock_t lock; /* protects everything except vcpus */
        int nmemslots;
        struct kvm_memory_slot memslots[KVM_MEMORY_SLOTS];
+       /*
+        * Hash table of struct kvm_mmu_page.
+        */
        struct list_head active_mmu_pages;
+       struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES];
        struct kvm_vcpu vcpus[KVM_MAX_VCPUS];
        int memory_config_version;
        int busy;
diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index da4d7dd..47c699c 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);
diff --git a/drivers/kvm/paging_tmpl.h b/drivers/kvm/paging_tmpl.h
index 11cac9d..f7cce44 100644
--- a/drivers/kvm/paging_tmpl.h
+++ b/drivers/kvm/paging_tmpl.h
@@ -32,6 +32,11 @@
        #define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
        #define PT_LEVEL_MASK(level) PT64_LEVEL_MASK(level)
        #define PT_PTE_COPY_MASK PT64_PTE_COPY_MASK
+       #ifdef CONFIG_X86_64
+       #define PT_MAX_FULL_LEVELS 4
+       #else
+       #define PT_MAX_FULL_LEVELS 2
+       #endif
 #elif PTTYPE == 32
        #define pt_element_t u32
        #define guest_walker guest_walker32
@@ -42,6 +47,7 @@
        #define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
        #define PT_LEVEL_MASK(level) PT32_LEVEL_MASK(level)
        #define PT_PTE_COPY_MASK PT32_PTE_COPY_MASK
+       #define PT_MAX_FULL_LEVELS 2
 #else
        #error Invalid PTTYPE value
 #endif
@@ -52,7 +58,7 @@
  */
 struct guest_walker {
        int level;
-       gfn_t table_gfn;
+       gfn_t table_gfn[PT_MAX_FULL_LEVELS];
        pt_element_t *table;
        pt_element_t *ptep;
        pt_element_t inherited_ar;
@@ -68,7 +74,9 @@ static void FNAME(walk_addr)(struct guest_walker *walker,
        struct kvm_memory_slot *slot;
        pt_element_t *ptep;
        pt_element_t root;
+       gfn_t table_gfn;
 
+       pgprintk("%s: addr %lx\n", __FUNCTION__, addr);
        walker->level = vcpu->mmu.root_level;
        walker->table = NULL;
        root = vcpu->cr3;
@@ -81,8 +89,11 @@ static void FNAME(walk_addr)(struct guest_walker *walker,
                --walker->level;
        }
 #endif
-       walker->table_gfn = (root & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
-       slot = gfn_to_memslot(vcpu->kvm, walker->table_gfn);
+       table_gfn = (root & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
+       walker->table_gfn[walker->level - 1] = table_gfn;
+       pgprintk("%s: table_gfn[%d] %lx\n", __FUNCTION__,
+                walker->level - 1, table_gfn);
+       slot = gfn_to_memslot(vcpu->kvm, table_gfn);
        hpa = safe_gpa_to_hpa(vcpu, root & PT64_BASE_ADDR_MASK);
        walker->table = kmap_atomic(pfn_to_page(hpa >> PAGE_SHIFT), KM_USER0);
 
@@ -111,12 +122,15 @@ static void FNAME(walk_addr)(struct guest_walker *walker,
 
                if (walker->level != 3 || is_long_mode(vcpu))
                        walker->inherited_ar &= walker->table[index];
-               walker->table_gfn = (*ptep & PT_BASE_ADDR_MASK) >> PAGE_SHIFT;
+               table_gfn = (*ptep & PT_BASE_ADDR_MASK) >> PAGE_SHIFT;
                paddr = safe_gpa_to_hpa(vcpu, *ptep & PT_BASE_ADDR_MASK);
                kunmap_atomic(walker->table, KM_USER0);
                walker->table = kmap_atomic(pfn_to_page(paddr >> PAGE_SHIFT),
                                            KM_USER0);
                --walker->level;
+               walker->table_gfn[walker->level - 1 ] = table_gfn;
+               pgprintk("%s: table_gfn[%d] %lx\n", __FUNCTION__,
+                        walker->level - 1, table_gfn);
        }
        walker->ptep = ptep;
 }
@@ -181,6 +195,8 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                u64 *shadow_ent = ((u64 *)__va(shadow_addr)) + index;
                struct kvm_mmu_page *shadow_page;
                u64 shadow_pte;
+               int metaphysical;
+               gfn_t table_gfn;
 
                if (is_present_pte(*shadow_ent) || is_io_pte(*shadow_ent)) {
                        if (level == PT_PAGE_TABLE_LEVEL)
@@ -205,7 +221,17 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                        return shadow_ent;
                }
 
-               shadow_page = kvm_mmu_alloc_page(vcpu, shadow_ent);
+               if (level - 1 == PT_PAGE_TABLE_LEVEL
+                   && walker->level == PT_DIRECTORY_LEVEL) {
+                       metaphysical = 1;
+                       table_gfn = (*guest_ent & PT_BASE_ADDR_MASK)
+                               >> PAGE_SHIFT;
+               } else {
+                       metaphysical = 0;
+                       table_gfn = walker->table_gfn[level - 2];
+               }
+               shadow_page = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
+                                              metaphysical, shadow_ent);
                if (!shadow_page)
                        return ERR_PTR(-ENOMEM);
                shadow_addr = shadow_page->page_hpa;
@@ -227,7 +253,8 @@ static int FNAME(fix_write_pf)(struct kvm_vcpu *vcpu,
                               u64 *shadow_ent,
                               struct guest_walker *walker,
                               gva_t addr,
-                              int user)
+                              int user,
+                              int *write_pt)
 {
        pt_element_t *guest_ent;
        int writable_shadow;
@@ -264,6 +291,12 @@ static int FNAME(fix_write_pf)(struct kvm_vcpu *vcpu,
        }
 
        gfn = (*guest_ent & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
+       if (kvm_mmu_lookup_page(vcpu, gfn)) {
+               pgprintk("%s: found shadow page for %lx, marking ro\n",
+                        __FUNCTION__, gfn);
+               *write_pt = 1;
+               return 0;
+       }
        mark_page_dirty(vcpu->kvm, gfn);
        *shadow_ent |= PT_WRITABLE_MASK;
        *guest_ent |= PT_DIRTY_MASK;
@@ -294,7 +327,9 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t 
addr,
        struct guest_walker walker;
        u64 *shadow_pte;
        int fixed;
+       int write_pt = 0;
 
+       pgprintk("%s: addr %lx err %x\n", __FUNCTION__, addr, error_code);
        /*
         * Look up the shadow pte for the faulting address.
         */
@@ -302,6 +337,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t 
addr,
                FNAME(walk_addr)(&walker, vcpu, addr);
                shadow_pte = FNAME(fetch)(vcpu, addr, &walker);
                if (IS_ERR(shadow_pte)) {  /* must be -ENOMEM */
+                       printk("%s: oom\n", __FUNCTION__);
                        nonpaging_flush(vcpu);
                        FNAME(release_walker)(&walker);
                        continue;
@@ -313,20 +349,27 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t 
addr,
         * The page is not mapped by the guest.  Let the guest handle it.
         */
        if (!shadow_pte) {
+               pgprintk("%s: not mapped\n", __FUNCTION__);
                inject_page_fault(vcpu, addr, error_code);
                FNAME(release_walker)(&walker);
                return 0;
        }
 
+       pgprintk("%s: shadow pte %p %llx\n", __FUNCTION__,
+                shadow_pte, *shadow_pte);
+
        /*
         * Update the shadow pte.
         */
        if (write_fault)
                fixed = FNAME(fix_write_pf)(vcpu, shadow_pte, &walker, addr,
-                                           user_fault);
+                                           user_fault, &write_pt);
        else
                fixed = fix_read_pf(shadow_pte);
 
+       pgprintk("%s: updated shadow pte %p %llx\n", __FUNCTION__,
+                shadow_pte, *shadow_pte);
+
        FNAME(release_walker)(&walker);
 
        /*
@@ -344,14 +387,14 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t 
addr,
        /*
         * pte not present, guest page fault.
         */
-       if (pte_present && !fixed) {
+       if (pte_present && !fixed && !write_pt) {
                inject_page_fault(vcpu, addr, error_code);
                return 0;
        }
 
        ++kvm_stat.pf_fixed;
 
-       return 0;
+       return write_pt;
 }
 
 static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr)
@@ -395,3 +438,4 @@ static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t 
vaddr)
 #undef PT_PTE_COPY_MASK
 #undef PT_NON_PTE_COPY_MASK
 #undef PT_DIR_BASE_ADDR_MASK
+#undef PT_MAX_FULL_LEVELS
-
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