[PATCH] KVM: MMU: Add shadow_accessed_shift

[yasker@gmail.com]

From: Sheng Yang <sheng.yang@intel.com>

We use a "fake" A/D bit for EPT, to keep epte behaviour consistent with shadow
spte. But it's not that good for MMU notifier. Now we can only expect return
young=0 for clean_flush_young() in most condition.

Also fix a unproper judgement based on shadow_accessed_mask=0 for EPT.

Signed-off-by: Sheng Yang <sheng.yang@intel.com>
---
 arch/x86/kvm/mmu.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 9bc31fc..1e9f9b4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -158,6 +158,7 @@ static u64 __read_mostly shadow_nx_mask;
 static u64 __read_mostly shadow_x_mask;	/* mutual exclusive with nx_mask */
 static u64 __read_mostly shadow_user_mask;
 static u64 __read_mostly shadow_accessed_mask;
+static u16 __read_mostly shadow_accessed_shift;
 static u64 __read_mostly shadow_dirty_mask;
 
 void kvm_mmu_set_nonpresent_ptes(u64 trap_pte, u64 notrap_pte)
@@ -178,6 +179,8 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
 {
 	shadow_user_mask = user_mask;
 	shadow_accessed_mask = accessed_mask;
+	shadow_accessed_shift = find_first_bit((unsigned long *)&accessed_mask,
+					       sizeof(accessed_mask));
 	shadow_dirty_mask = dirty_mask;
 	shadow_nx_mask = nx_mask;
 	shadow_x_mask = x_mask;
@@ -716,10 +719,10 @@ static int kvm_age_rmapp(struct kvm *kvm, unsigned long *rmapp)
 		int _young;
 		u64 _spte = *spte;
 		BUG_ON(!(_spte & PT_PRESENT_MASK));
-		_young = _spte & PT_ACCESSED_MASK;
+		_young = _spte & shadow_accessed_mask;
 		if (_young) {
 			young = 1;
-			clear_bit(PT_ACCESSED_SHIFT, (unsigned long *)spte);
+			clear_bit(shadow_accessed_shift, (unsigned long *)spte);
 		}
 		spte = rmap_next(kvm, rmapp, spte);
 	}
@@ -1789,10 +1792,9 @@ static void kvm_mmu_access_page(struct kvm_vcpu *vcpu, gfn_t gfn)
 
 	if (spte
 	    && vcpu->arch.last_pte_gfn == gfn
-	    && shadow_accessed_mask
 	    && !(*spte & shadow_accessed_mask)
 	    && is_shadow_present_pte(*spte))
-		set_bit(PT_ACCESSED_SHIFT, (unsigned long *)spte);
+		set_bit(shadow_accessed_shift, (unsigned long *)spte);
 }
 
 void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
-- 
1.5.3