1 files changed, 356 insertions, 153 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 7012de4a1fed..2fd7586aad4d 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -37,6 +37,8 @@
 #include <linux/srcu.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
+#include <linux/hash.h>
+#include <linux/kern_levels.h>
 
 #include <asm/page.h>
 #include <asm/cmpxchg.h>
@@ -129,6 +131,10 @@ module_param(dbg, bool, 0644);
 #define ACC_USER_MASK    PT_USER_MASK
 #define ACC_ALL          (ACC_EXEC_MASK | ACC_WRITE_MASK | ACC_USER_MASK)
 
+/* The mask for the R/X bits in EPT PTEs */
+#define PT64_EPT_READABLE_MASK			0x1ull
+#define PT64_EPT_EXECUTABLE_MASK		0x4ull
+
 #include <trace/events/kvm.h>
 
 #define CREATE_TRACE_POINTS
@@ -178,15 +184,40 @@ static u64 __read_mostly shadow_dirty_mask;
 static u64 __read_mostly shadow_mmio_mask;
 static u64 __read_mostly shadow_present_mask;
 
+/*
+ * The mask/value to distinguish a PTE that has been marked not-present for
+ * access tracking purposes.
+ * The mask would be either 0 if access tracking is disabled, or
+ * SPTE_SPECIAL_MASK|VMX_EPT_RWX_MASK if access tracking is enabled.
+ */
+static u64 __read_mostly shadow_acc_track_mask;
+static const u64 shadow_acc_track_value = SPTE_SPECIAL_MASK;
+
+/*
+ * The mask/shift to use for saving the original R/X bits when marking the PTE
+ * as not-present for access tracking purposes. We do not save the W bit as the
+ * PTEs being access tracked also need to be dirty tracked, so the W bit will be
+ * restored only when a write is attempted to the page.
+ */
+static const u64 shadow_acc_track_saved_bits_mask = PT64_EPT_READABLE_MASK |
+						    PT64_EPT_EXECUTABLE_MASK;
+static const u64 shadow_acc_track_saved_bits_shift = PT64_SECOND_AVAIL_BITS_SHIFT;
+
 static void mmu_spte_set(u64 *sptep, u64 spte);
 static void mmu_free_roots(struct kvm_vcpu *vcpu);
 
 void kvm_mmu_set_mmio_spte_mask(u64 mmio_mask)
 {
-	shadow_mmio_mask = mmio_mask;
+	shadow_mmio_mask = mmio_mask | SPTE_SPECIAL_MASK;
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_set_mmio_spte_mask);
 
+static inline bool is_access_track_spte(u64 spte)
+{
+	/* Always false if shadow_acc_track_mask is zero.  */
+	return (spte & shadow_acc_track_mask) == shadow_acc_track_value;
+}
+
 /*
  * the low bit of the generation number is always presumed to be zero.
  * This disables mmio caching during memslot updates.  The concept is
@@ -284,17 +315,35 @@ static bool check_mmio_spte(struct kvm_vcpu *vcpu, u64 spte)
 }
 
 void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
-		u64 dirty_mask, u64 nx_mask, u64 x_mask, u64 p_mask)
+		u64 dirty_mask, u64 nx_mask, u64 x_mask, u64 p_mask,
+		u64 acc_track_mask)
 {
+	if (acc_track_mask != 0)
+		acc_track_mask |= SPTE_SPECIAL_MASK;
+
 	shadow_user_mask = user_mask;
 	shadow_accessed_mask = accessed_mask;
 	shadow_dirty_mask = dirty_mask;
 	shadow_nx_mask = nx_mask;
 	shadow_x_mask = x_mask;
 	shadow_present_mask = p_mask;
+	shadow_acc_track_mask = acc_track_mask;
+	WARN_ON(shadow_accessed_mask != 0 && shadow_acc_track_mask != 0);
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_set_mask_ptes);
 
+void kvm_mmu_clear_all_pte_masks(void)
+{
+	shadow_user_mask = 0;
+	shadow_accessed_mask = 0;
+	shadow_dirty_mask = 0;
+	shadow_nx_mask = 0;
+	shadow_x_mask = 0;
+	shadow_mmio_mask = 0;
+	shadow_present_mask = 0;
+	shadow_acc_track_mask = 0;
+}
+
 static int is_cpuid_PSE36(void)
 {
 	return 1;
@@ -307,7 +356,7 @@ static int is_nx(struct kvm_vcpu *vcpu)
 
 static int is_shadow_present_pte(u64 pte)
 {
-	return (pte & 0xFFFFFFFFull) && !is_mmio_spte(pte);
+	return (pte != 0) && !is_mmio_spte(pte);
 }
 
 static int is_large_pte(u64 pte)
@@ -324,6 +373,11 @@ static int is_last_spte(u64 pte, int level)
 	return 0;
 }
 
+static bool is_executable_pte(u64 spte)
+{
+	return (spte & (shadow_x_mask | shadow_nx_mask)) == shadow_x_mask;
+}
+
 static kvm_pfn_t spte_to_pfn(u64 pte)
 {
 	return (pte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
@@ -473,7 +527,7 @@ retry:
 }
 #endif
 
-static bool spte_is_locklessly_modifiable(u64 spte)
+static bool spte_can_locklessly_be_made_writable(u64 spte)
 {
 	return (spte & (SPTE_HOST_WRITEABLE | SPTE_MMU_WRITEABLE)) ==
 		(SPTE_HOST_WRITEABLE | SPTE_MMU_WRITEABLE);
@@ -481,36 +535,38 @@ static bool spte_is_locklessly_modifiable(u64 spte)
 
 static bool spte_has_volatile_bits(u64 spte)
 {
+	if (!is_shadow_present_pte(spte))
+		return false;
+
 	/*
 	 * Always atomically update spte if it can be updated
 	 * out of mmu-lock, it can ensure dirty bit is not lost,
 	 * also, it can help us to get a stable is_writable_pte()
 	 * to ensure tlb flush is not missed.
 	 */
-	if (spte_is_locklessly_modifiable(spte))
+	if (spte_can_locklessly_be_made_writable(spte) ||
+	    is_access_track_spte(spte))
 		return true;
 
-	if (!shadow_accessed_mask)
-		return false;
-
-	if (!is_shadow_present_pte(spte))
-		return false;
-
-	if ((spte & shadow_accessed_mask) &&
-	      (!is_writable_pte(spte) || (spte & shadow_dirty_mask)))
-		return false;
+	if (shadow_accessed_mask) {
+		if ((spte & shadow_accessed_mask) == 0 ||
+	    	    (is_writable_pte(spte) && (spte & shadow_dirty_mask) == 0))
+			return true;
+	}
 
-	return true;
+	return false;
 }
 
-static bool spte_is_bit_cleared(u64 old_spte, u64 new_spte, u64 bit_mask)
+static bool is_accessed_spte(u64 spte)
 {
-	return (old_spte & bit_mask) && !(new_spte & bit_mask);
+	return shadow_accessed_mask ? spte & shadow_accessed_mask
+				    : !is_access_track_spte(spte);
 }
 
-static bool spte_is_bit_changed(u64 old_spte, u64 new_spte, u64 bit_mask)
+static bool is_dirty_spte(u64 spte)
 {
-	return (old_spte & bit_mask) != (new_spte & bit_mask);
+	return shadow_dirty_mask ? spte & shadow_dirty_mask
+				 : spte & PT_WRITABLE_MASK;
 }
 
 /* Rules for using mmu_spte_set:
@@ -525,25 +581,19 @@ static void mmu_spte_set(u64 *sptep, u64 new_spte)
 	__set_spte(sptep, new_spte);
 }
 
-/* Rules for using mmu_spte_update:
- * Update the state bits, it means the mapped pfn is not changed.
- *
- * Whenever we overwrite a writable spte with a read-only one we
- * should flush remote TLBs. Otherwise rmap_write_protect
- * will find a read-only spte, even though the writable spte
- * might be cached on a CPU's TLB, the return value indicates this
- * case.
+/*
+ * Update the SPTE (excluding the PFN), but do not track changes in its
+ * accessed/dirty status.
  */
-static bool mmu_spte_update(u64 *sptep, u64 new_spte)
+static u64 mmu_spte_update_no_track(u64 *sptep, u64 new_spte)
 {
 	u64 old_spte = *sptep;
-	bool ret = false;
 
 	WARN_ON(!is_shadow_present_pte(new_spte));
 
 	if (!is_shadow_present_pte(old_spte)) {
 		mmu_spte_set(sptep, new_spte);
-		return ret;
+		return old_spte;
 	}
 
 	if (!spte_has_volatile_bits(old_spte))
@@ -551,45 +601,62 @@ static bool mmu_spte_update(u64 *sptep, u64 new_spte)
 	else
 		old_spte = __update_clear_spte_slow(sptep, new_spte);
 
+	WARN_ON(spte_to_pfn(old_spte) != spte_to_pfn(new_spte));
+
+	return old_spte;
+}
+
+/* Rules for using mmu_spte_update:
+ * Update the state bits, it means the mapped pfn is not changed.
+ *
+ * Whenever we overwrite a writable spte with a read-only one we
+ * should flush remote TLBs. Otherwise rmap_write_protect
+ * will find a read-only spte, even though the writable spte
+ * might be cached on a CPU's TLB, the return value indicates this
+ * case.
+ *
+ * Returns true if the TLB needs to be flushed
+ */
+static bool mmu_spte_update(u64 *sptep, u64 new_spte)
+{
+	bool flush = false;
+	u64 old_spte = mmu_spte_update_no_track(sptep, new_spte);
+
+	if (!is_shadow_present_pte(old_spte))
+		return false;
+
 	/*
 	 * For the spte updated out of mmu-lock is safe, since
 	 * we always atomically update it, see the comments in
 	 * spte_has_volatile_bits().
 	 */
-	if (spte_is_locklessly_modifiable(old_spte) &&
+	if (spte_can_locklessly_be_made_writable(old_spte) &&
 	      !is_writable_pte(new_spte))
-		ret = true;
-
-	if (!shadow_accessed_mask) {
-		/*
-		 * We don't set page dirty when dropping non-writable spte.
-		 * So do it now if the new spte is becoming non-writable.
-		 */
-		if (ret)
-			kvm_set_pfn_dirty(spte_to_pfn(old_spte));
-		return ret;
-	}
+		flush = true;
 
 	/*
-	 * Flush TLB when accessed/dirty bits are changed in the page tables,
+	 * Flush TLB when accessed/dirty states are changed in the page tables,
 	 * to guarantee consistency between TLB and page tables.
 	 */
-	if (spte_is_bit_changed(old_spte, new_spte,
-                                shadow_accessed_mask | shadow_dirty_mask))
-		ret = true;
 
-	if (spte_is_bit_cleared(old_spte, new_spte, shadow_accessed_mask))
+	if (is_accessed_spte(old_spte) && !is_accessed_spte(new_spte)) {
+		flush = true;
 		kvm_set_pfn_accessed(spte_to_pfn(old_spte));
-	if (spte_is_bit_cleared(old_spte, new_spte, shadow_dirty_mask))
+	}
+
+	if (is_dirty_spte(old_spte) && !is_dirty_spte(new_spte)) {
+		flush = true;
 		kvm_set_pfn_dirty(spte_to_pfn(old_spte));
+	}
 
-	return ret;
+	return flush;
 }
 
 /*
  * Rules for using mmu_spte_clear_track_bits:
  * It sets the sptep from present to nonpresent, and track the
  * state bits, it is used to clear the last level sptep.
+ * Returns non-zero if the PTE was previously valid.
  */
 static int mmu_spte_clear_track_bits(u64 *sptep)
 {
@@ -613,11 +680,12 @@ static int mmu_spte_clear_track_bits(u64 *sptep)
 	 */
 	WARN_ON(!kvm_is_reserved_pfn(pfn) && !page_count(pfn_to_page(pfn)));
 
-	if (!shadow_accessed_mask || old_spte & shadow_accessed_mask)
+	if (is_accessed_spte(old_spte))
 		kvm_set_pfn_accessed(pfn);
-	if (old_spte & (shadow_dirty_mask ? shadow_dirty_mask :
-					    PT_WRITABLE_MASK))
+
+	if (is_dirty_spte(old_spte))
 		kvm_set_pfn_dirty(pfn);
+
 	return 1;
 }
 
@@ -636,6 +704,78 @@ static u64 mmu_spte_get_lockless(u64 *sptep)
 	return __get_spte_lockless(sptep);
 }
 
+static u64 mark_spte_for_access_track(u64 spte)
+{
+	if (shadow_accessed_mask != 0)
+		return spte & ~shadow_accessed_mask;
+
+	if (shadow_acc_track_mask == 0 || is_access_track_spte(spte))
+		return spte;
+
+	/*
+	 * Making an Access Tracking PTE will result in removal of write access
+	 * from the PTE. So, verify that we will be able to restore the write
+	 * access in the fast page fault path later on.
+	 */
+	WARN_ONCE((spte & PT_WRITABLE_MASK) &&
+		  !spte_can_locklessly_be_made_writable(spte),
+		  "kvm: Writable SPTE is not locklessly dirty-trackable\n");
+
+	WARN_ONCE(spte & (shadow_acc_track_saved_bits_mask <<
+			  shadow_acc_track_saved_bits_shift),
+		  "kvm: Access Tracking saved bit locations are not zero\n");
+
+	spte |= (spte & shadow_acc_track_saved_bits_mask) <<
+		shadow_acc_track_saved_bits_shift;
+	spte &= ~shadow_acc_track_mask;
+	spte |= shadow_acc_track_value;
+
+	return spte;
+}
+
+/* Restore an acc-track PTE back to a regular PTE */
+static u64 restore_acc_track_spte(u64 spte)
+{
+	u64 new_spte = spte;
+	u64 saved_bits = (spte >> shadow_acc_track_saved_bits_shift)
+			 & shadow_acc_track_saved_bits_mask;
+
+	WARN_ON_ONCE(!is_access_track_spte(spte));
+
+	new_spte &= ~shadow_acc_track_mask;
+	new_spte &= ~(shadow_acc_track_saved_bits_mask <<
+		      shadow_acc_track_saved_bits_shift);
+	new_spte |= saved_bits;
+
+	return new_spte;
+}
+
+/* Returns the Accessed status of the PTE and resets it at the same time. */
+static bool mmu_spte_age(u64 *sptep)
+{
+	u64 spte = mmu_spte_get_lockless(sptep);
+
+	if (!is_accessed_spte(spte))
+		return false;
+
+	if (shadow_accessed_mask) {
+		clear_bit((ffs(shadow_accessed_mask) - 1),
+			  (unsigned long *)sptep);
+	} else {
+		/*
+		 * Capture the dirty status of the page, so that it doesn't get
+		 * lost when the SPTE is marked for access tracking.
+		 */
+		if (is_writable_pte(spte))
+			kvm_set_pfn_dirty(spte_to_pfn(spte));
+
+		spte = mark_spte_for_access_track(spte);
+		mmu_spte_update_no_track(sptep, spte);
+	}
+
+	return true;
+}
+
 static void walk_shadow_page_lockless_begin(struct kvm_vcpu *vcpu)
 {
 	/*
@@ -1212,7 +1352,7 @@ static bool spte_write_protect(u64 *sptep, bool pt_protect)
 	u64 spte = *sptep;
 
 	if (!is_writable_pte(spte) &&
-	      !(pt_protect && spte_is_locklessly_modifiable(spte)))
+	      !(pt_protect && spte_can_locklessly_be_made_writable(spte)))
 		return false;
 
 	rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep);
@@ -1420,7 +1560,7 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
 restart:
 	for_each_rmap_spte(rmap_head, &iter, sptep) {
 		rmap_printk("kvm_set_pte_rmapp: spte %p %llx gfn %llx (%d)\n",
-			     sptep, *sptep, gfn, level);
+			    sptep, *sptep, gfn, level);
 
 		need_flush = 1;
 
@@ -1433,7 +1573,8 @@ restart:
 
 			new_spte &= ~PT_WRITABLE_MASK;
 			new_spte &= ~SPTE_HOST_WRITEABLE;
-			new_spte &= ~shadow_accessed_mask;
+
+			new_spte = mark_spte_for_access_track(new_spte);
 
 			mmu_spte_clear_track_bits(sptep);
 			mmu_spte_set(sptep, new_spte);
@@ -1595,15 +1736,8 @@ static int kvm_age_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
 	struct rmap_iterator uninitialized_var(iter);
 	int young = 0;
 
-	BUG_ON(!shadow_accessed_mask);
-
-	for_each_rmap_spte(rmap_head, &iter, sptep) {
-		if (*sptep & shadow_accessed_mask) {
-			young = 1;
-			clear_bit((ffs(shadow_accessed_mask) - 1),
-				 (unsigned long *)sptep);
-		}
-	}
+	for_each_rmap_spte(rmap_head, &iter, sptep)
+		young |= mmu_spte_age(sptep);
 
 	trace_kvm_age_page(gfn, level, slot, young);
 	return young;
@@ -1615,24 +1749,20 @@ static int kvm_test_age_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
 {
 	u64 *sptep;
 	struct rmap_iterator iter;
-	int young = 0;
 
 	/*
-	 * If there's no access bit in the secondary pte set by the
-	 * hardware it's up to gup-fast/gup to set the access bit in
-	 * the primary pte or in the page structure.
+	 * If there's no access bit in the secondary pte set by the hardware and
+	 * fast access tracking is also not enabled, it's up to gup-fast/gup to
+	 * set the access bit in the primary pte or in the page structure.
 	 */
-	if (!shadow_accessed_mask)
+	if (!shadow_accessed_mask && !shadow_acc_track_mask)
 		goto out;
 
-	for_each_rmap_spte(rmap_head, &iter, sptep) {
-		if (*sptep & shadow_accessed_mask) {
-			young = 1;
-			break;
-		}
-	}
+	for_each_rmap_spte(rmap_head, &iter, sptep)
+		if (is_accessed_spte(*sptep))
+			return 1;
 out:
-	return young;
+	return 0;
 }
 
 #define RMAP_RECYCLE_THRESHOLD 1000
@@ -1660,7 +1790,7 @@ int kvm_age_hva(struct kvm *kvm, unsigned long start, unsigned long end)
 	 * This has some overhead, but not as much as the cost of swapping
 	 * out actively used pages or breaking up actively used hugepages.
 	 */
-	if (!shadow_accessed_mask)
+	if (!shadow_accessed_mask && !shadow_acc_track_mask)
 		return kvm_handle_hva_range(kvm, start, end, 0,
 					    kvm_unmap_rmapp);
 
@@ -1713,7 +1843,7 @@ static void kvm_mmu_free_page(struct kvm_mmu_page *sp)
 
 static unsigned kvm_page_table_hashfn(gfn_t gfn)
 {
-	return gfn & ((1 << KVM_MMU_HASH_SHIFT) - 1);
+	return hash_64(gfn, KVM_MMU_HASH_SHIFT);
 }
 
 static void mmu_page_add_parent_pte(struct kvm_vcpu *vcpu,
@@ -1904,17 +2034,17 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
  * since it has been deleted from active_mmu_pages but still can be found
  * at hast list.
  *
- * for_each_gfn_valid_sp() has skipped that kind of pages.
+ * for_each_valid_sp() has skipped that kind of pages.
  */
-#define for_each_gfn_valid_sp(_kvm, _sp, _gfn)				\
+#define for_each_valid_sp(_kvm, _sp, _gfn)				\
 	hlist_for_each_entry(_sp,					\
 	  &(_kvm)->arch.mmu_page_hash[kvm_page_table_hashfn(_gfn)], hash_link) \
-		if ((_sp)->gfn != (_gfn) || is_obsolete_sp((_kvm), (_sp)) \
-			|| (_sp)->role.invalid) {} else
+		if (is_obsolete_sp((_kvm), (_sp)) || (_sp)->role.invalid) {    \
+		} else
 
 #define for_each_gfn_indirect_valid_sp(_kvm, _sp, _gfn)			\
-	for_each_gfn_valid_sp(_kvm, _sp, _gfn)				\
-		if ((_sp)->role.direct) {} else
+	for_each_valid_sp(_kvm, _sp, _gfn)				\
+		if ((_sp)->gfn != (_gfn) || (_sp)->role.direct) {} else
 
 /* @sp->gfn should be write-protected at the call site */
 static bool __kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
@@ -2116,6 +2246,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 	struct kvm_mmu_page *sp;
 	bool need_sync = false;
 	bool flush = false;
+	int collisions = 0;
 	LIST_HEAD(invalid_list);
 
 	role = vcpu->arch.mmu.base_role;
@@ -2130,7 +2261,12 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 		quadrant &= (1 << ((PT32_PT_BITS - PT64_PT_BITS) * level)) - 1;
 		role.quadrant = quadrant;
 	}
-	for_each_gfn_valid_sp(vcpu->kvm, sp, gfn) {
+	for_each_valid_sp(vcpu->kvm, sp, gfn) {
+		if (sp->gfn != gfn) {
+			collisions++;
+			continue;
+		}
+
 		if (!need_sync && sp->unsync)
 			need_sync = true;
 
@@ -2153,7 +2289,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 
 		__clear_sp_write_flooding_count(sp);
 		trace_kvm_mmu_get_page(sp, false);
-		return sp;
+		goto out;
 	}
 
 	++vcpu->kvm->stat.mmu_cache_miss;
@@ -2183,6 +2319,9 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 	trace_kvm_mmu_get_page(sp, true);
 
 	kvm_mmu_flush_or_zap(vcpu, &invalid_list, false, flush);
+out:
+	if (collisions > vcpu->kvm->stat.max_mmu_page_hash_collisions)
+		vcpu->kvm->stat.max_mmu_page_hash_collisions = collisions;
 	return sp;
 }
 
@@ -2583,6 +2722,9 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 		spte |= shadow_dirty_mask;
 	}
 
+	if (speculative)
+		spte = mark_spte_for_access_track(spte);
+
 set_pte:
 	if (mmu_spte_update(sptep, spte))
 		kvm_flush_remote_tlbs(vcpu->kvm);
@@ -2636,7 +2778,7 @@ static bool mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep, unsigned pte_access,
 	pgprintk("%s: setting spte %llx\n", __func__, *sptep);
 	pgprintk("instantiating %s PTE (%s) at %llx (%llx) addr %p\n",
 		 is_large_pte(*sptep)? "2MB" : "4kB",
-		 *sptep & PT_PRESENT_MASK ?"RW":"R", gfn,
+		 *sptep & PT_WRITABLE_MASK ? "RW" : "R", gfn,
 		 *sptep, sptep);
 	if (!was_rmapped && is_large_pte(*sptep))
 		++vcpu->kvm->stat.lpages;
@@ -2869,33 +3011,43 @@ static bool page_fault_can_be_fast(u32 error_code)
 	if (unlikely(error_code & PFERR_RSVD_MASK))
 		return false;
 
+	/* See if the page fault is due to an NX violation */
+	if (unlikely(((error_code & (PFERR_FETCH_MASK | PFERR_PRESENT_MASK))
+		      == (PFERR_FETCH_MASK | PFERR_PRESENT_MASK))))
+		return false;
+
 	/*
-	 * #PF can be fast only if the shadow page table is present and it
-	 * is caused by write-protect, that means we just need change the
-	 * W bit of the spte which can be done out of mmu-lock.
+	 * #PF can be fast if:
+	 * 1. The shadow page table entry is not present, which could mean that
+	 *    the fault is potentially caused by access tracking (if enabled).
+	 * 2. The shadow page table entry is present and the fault
+	 *    is caused by write-protect, that means we just need change the W
+	 *    bit of the spte which can be done out of mmu-lock.
+	 *
+	 * However, if access tracking is disabled we know that a non-present
+	 * page must be a genuine page fault where we have to create a new SPTE.
+	 * So, if access tracking is disabled, we return true only for write
+	 * accesses to a present page.
 	 */
-	if (!(error_code & PFERR_PRESENT_MASK) ||
-	      !(error_code & PFERR_WRITE_MASK))
-		return false;
 
-	return true;
+	return shadow_acc_track_mask != 0 ||
+	       ((error_code & (PFERR_WRITE_MASK | PFERR_PRESENT_MASK))
+		== (PFERR_WRITE_MASK | PFERR_PRESENT_MASK));
 }
 
+/*
+ * Returns true if the SPTE was fixed successfully. Otherwise,
+ * someone else modified the SPTE from its original value.
+ */
 static bool
 fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
-			u64 *sptep, u64 spte)
+			u64 *sptep, u64 old_spte, u64 new_spte)
 {
 	gfn_t gfn;
 
 	WARN_ON(!sp->role.direct);
 
 	/*
-	 * The gfn of direct spte is stable since it is calculated
-	 * by sp->gfn.
-	 */
-	gfn = kvm_mmu_page_get_gfn(sp, sptep - sp->spt);
-
-	/*
 	 * Theoretically we could also set dirty bit (and flush TLB) here in
 	 * order to eliminate unnecessary PML logging. See comments in
 	 * set_spte. But fast_page_fault is very unlikely to happen with PML
@@ -2907,12 +3059,33 @@ fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
 	 *
 	 * Compare with set_spte where instead shadow_dirty_mask is set.
 	 */
-	if (cmpxchg64(sptep, spte, spte | PT_WRITABLE_MASK) == spte)
+	if (cmpxchg64(sptep, old_spte, new_spte) != old_spte)
+		return false;
+
+	if (is_writable_pte(new_spte) && !is_writable_pte(old_spte)) {
+		/*
+		 * The gfn of direct spte is stable since it is
+		 * calculated by sp->gfn.
+		 */
+		gfn = kvm_mmu_page_get_gfn(sp, sptep - sp->spt);
 		kvm_vcpu_mark_page_dirty(vcpu, gfn);
+	}
 
 	return true;
 }
 
+static bool is_access_allowed(u32 fault_err_code, u64 spte)
+{
+	if (fault_err_code & PFERR_FETCH_MASK)
+		return is_executable_pte(spte);
+
+	if (fault_err_code & PFERR_WRITE_MASK)
+		return is_writable_pte(spte);
+
+	/* Fault was on Read access */
+	return spte & PT_PRESENT_MASK;
+}
+
 /*
  * Return value:
  * - true: let the vcpu to access on the same address again.
@@ -2923,8 +3096,9 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
 {
 	struct kvm_shadow_walk_iterator iterator;
 	struct kvm_mmu_page *sp;
-	bool ret = false;
+	bool fault_handled = false;
 	u64 spte = 0ull;
+	uint retry_count = 0;
 
 	if (!VALID_PAGE(vcpu->arch.mmu.root_hpa))
 		return false;
@@ -2933,66 +3107,93 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
 		return false;
 
 	walk_shadow_page_lockless_begin(vcpu);
-	for_each_shadow_entry_lockless(vcpu, gva, iterator, spte)
-		if (!is_shadow_present_pte(spte) || iterator.level < level)
+
+	do {
+		u64 new_spte;
+
+		for_each_shadow_entry_lockless(vcpu, gva, iterator, spte)
+			if (!is_shadow_present_pte(spte) ||
+			    iterator.level < level)
+				break;
+
+		sp = page_header(__pa(iterator.sptep));
+		if (!is_last_spte(spte, sp->role.level))
 			break;
 
-	/*
-	 * If the mapping has been changed, let the vcpu fault on the
-	 * same address again.
-	 */
-	if (!is_shadow_present_pte(spte)) {
-		ret = true;
-		goto exit;
-	}
+		/*
+		 * Check whether the memory access that caused the fault would
+		 * still cause it if it were to be performed right now. If not,
+		 * then this is a spurious fault caused by TLB lazily flushed,
+		 * or some other CPU has already fixed the PTE after the
+		 * current CPU took the fault.
+		 *
+		 * Need not check the access of upper level table entries since
+		 * they are always ACC_ALL.
+		 */
+		if (is_access_allowed(error_code, spte)) {
+			fault_handled = true;
+			break;
+		}
 
-	sp = page_header(__pa(iterator.sptep));
-	if (!is_last_spte(spte, sp->role.level))
-		goto exit;
+		new_spte = spte;
 
-	/*
-	 * Check if it is a spurious fault caused by TLB lazily flushed.
-	 *
-	 * Need not check the access of upper level table entries since
-	 * they are always ACC_ALL.
-	 */
-	 if (is_writable_pte(spte)) {
-		ret = true;
-		goto exit;
-	}
+		if (is_access_track_spte(spte))
+			new_spte = restore_acc_track_spte(new_spte);
 
-	/*
-	 * Currently, to simplify the code, only the spte write-protected
-	 * by dirty-log can be fast fixed.
-	 */
-	if (!spte_is_locklessly_modifiable(spte))
-		goto exit;
+		/*
+		 * Currently, to simplify the code, write-protection can
+		 * be removed in the fast path only if the SPTE was
+		 * write-protected for dirty-logging or access tracking.
+		 */
+		if ((error_code & PFERR_WRITE_MASK) &&
+		    spte_can_locklessly_be_made_writable(spte))
+		{
+			new_spte |= PT_WRITABLE_MASK;
 
-	/*
-	 * Do not fix write-permission on the large spte since we only dirty
-	 * the first page into the dirty-bitmap in fast_pf_fix_direct_spte()
-	 * that means other pages are missed if its slot is dirty-logged.
-	 *
-	 * Instead, we let the slow page fault path create a normal spte to
-	 * fix the access.
-	 *
-	 * See the comments in kvm_arch_commit_memory_region().
-	 */
-	if (sp->role.level > PT_PAGE_TABLE_LEVEL)
-		goto exit;
+			/*
+			 * Do not fix write-permission on the large spte.  Since
+			 * we only dirty the first page into the dirty-bitmap in
+			 * fast_pf_fix_direct_spte(), other pages are missed
+			 * if its slot has dirty logging enabled.
+			 *
+			 * Instead, we let the slow page fault path create a
+			 * normal spte to fix the access.
+			 *
+			 * See the comments in kvm_arch_commit_memory_region().
+			 */
+			if (sp->role.level > PT_PAGE_TABLE_LEVEL)
+				break;
+		}
+
+		/* Verify that the fault can be handled in the fast path */
+		if (new_spte == spte ||
+		    !is_access_allowed(error_code, new_spte))
+			break;
+
+		/*
+		 * Currently, fast page fault only works for direct mapping
+		 * since the gfn is not stable for indirect shadow page. See
+		 * Documentation/virtual/kvm/locking.txt to get more detail.
+		 */
+		fault_handled = fast_pf_fix_direct_spte(vcpu, sp,
+							iterator.sptep, spte,
+							new_spte);
+		if (fault_handled)
+			break;
+
+		if (++retry_count > 4) {
+			printk_once(KERN_WARNING
+				"kvm: Fast #PF retrying more than 4 times.\n");
+			break;
+		}
+
+	} while (true);
 
-	/*
-	 * Currently, fast page fault only works for direct mapping since
-	 * the gfn is not stable for indirect shadow page.
-	 * See Documentation/virtual/kvm/locking.txt to get more detail.
-	 */
-	ret = fast_pf_fix_direct_spte(vcpu, sp, iterator.sptep, spte);
-exit:
 	trace_fast_page_fault(vcpu, gva, error_code, iterator.sptep,
-			      spte, ret);
+			      spte, fault_handled);
 	walk_shadow_page_lockless_end(vcpu);
 
-	return ret;
+	return fault_handled;
 }
 
 static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
@@ -5063,6 +5264,8 @@ static void mmu_destroy_caches(void)
 
 int kvm_mmu_module_init(void)
 {
+	kvm_mmu_clear_all_pte_masks();
+
 	pte_list_desc_cache = kmem_cache_create("pte_list_desc",
 					    sizeof(struct pte_list_desc),
 					    0, 0, NULL);