KVM: MMU: mark page dirty only when page is really written

Mark page dirty only when this page is really written, it's more exacter,
and also can fix dirty page marking in speculation path
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/mmu.c

@@ -307,24 +307,42 @@ static bool spte_has_volatile_bits(u64 spte)
 	if (!is_shadow_present_pte(spte))
 		return false;
 
-	if (spte & shadow_accessed_mask)
+	if ((spte & shadow_accessed_mask) &&
+	      (!is_writable_pte(spte) || (spte & shadow_dirty_mask)))
 		return false;
 
 	return true;
 }
 
+static bool spte_is_bit_cleared(u64 old_spte, u64 new_spte, u64 bit_mask)
+{
+	return (old_spte & bit_mask) && !(new_spte & bit_mask);
+}
+
 static void update_spte(u64 *sptep, u64 new_spte)
 {
-	u64 old_spte;
+	u64 mask, old_spte = *sptep;
+
+	WARN_ON(!is_rmap_spte(new_spte));
+
+	new_spte |= old_spte & shadow_dirty_mask;
 
-	if (!shadow_accessed_mask || (new_spte & shadow_accessed_mask) ||
-	      !is_rmap_spte(*sptep))
+	mask = shadow_accessed_mask;
+	if (is_writable_pte(old_spte))
+		mask |= shadow_dirty_mask;
+
+	if (!spte_has_volatile_bits(old_spte) || (new_spte & mask) == mask)
 		__set_spte(sptep, new_spte);
-	else {
+	else
 		old_spte = __xchg_spte(sptep, new_spte);
-		if (old_spte & shadow_accessed_mask)
+
+	if (!shadow_accessed_mask)
+		return;
+
+	if (spte_is_bit_cleared(old_spte, new_spte, shadow_accessed_mask))
 		kvm_set_pfn_accessed(spte_to_pfn(old_spte));
-	}
+	if (spte_is_bit_cleared(old_spte, new_spte, shadow_dirty_mask))
+		kvm_set_pfn_dirty(spte_to_pfn(old_spte));
 }
 
 static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
@@ -704,7 +722,7 @@ static void set_spte_track_bits(u64 *sptep, u64 new_spte)
 	pfn = spte_to_pfn(old_spte);
 	if (!shadow_accessed_mask || old_spte & shadow_accessed_mask)
 		kvm_set_pfn_accessed(pfn);
-	if (is_writable_pte(old_spte))
+	if (!shadow_dirty_mask || (old_spte & shadow_dirty_mask))
 		kvm_set_pfn_dirty(pfn);
 }
 
@@ -759,13 +777,6 @@ static int rmap_write_protect(struct kvm *kvm, u64 gfn)
 		}
 		spte = rmap_next(kvm, rmapp, spte);
 	}
-	if (write_protected) {
-		pfn_t pfn;
-
-		spte = rmap_next(kvm, rmapp, NULL);
-		pfn = spte_to_pfn(*spte);
-		kvm_set_pfn_dirty(pfn);
-	}
 
 	/* check for huge page mappings */
 	for (i = PT_DIRECTORY_LEVEL;
@@ -1938,7 +1949,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 	 * whether the guest actually used the pte (in order to detect
 	 * demand paging).
 	 */
-	spte = shadow_base_present_pte | shadow_dirty_mask;
+	spte = shadow_base_present_pte;
 	if (!speculative)
 		spte |= shadow_accessed_mask;
 	if (!dirty)
@@ -1999,8 +2010,6 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 		mark_page_dirty(vcpu->kvm, gfn);
 
 set_pte:
-	if (is_writable_pte(*sptep) && !is_writable_pte(spte))
-		kvm_set_pfn_dirty(pfn);
 	update_spte(sptep, spte);
 done:
 	return ret;