[PATCH v3 4/9] KVM: MMU: introduce SPTE_ALLOW_WRITE bit

[Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>]

This bit indicates whether the spte is allow to be writable that
means the gpte of this spte is writable and the pfn pointed by
this spte is writable on host

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
---
 arch/x86/kvm/mmu.c |   13 ++++++-------
 1 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index e70ff38..dd984b6 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -145,7 +145,8 @@ module_param(dbg, bool, 0644);
 #define CREATE_TRACE_POINTS
 #include "mmutrace.h"

-#define SPTE_HOST_WRITEABLE (1ULL << PT_FIRST_AVAIL_BITS_SHIFT)
+#define SPTE_HOST_WRITEABLE	(1ULL << PT_FIRST_AVAIL_BITS_SHIFT)
+#define SPTE_ALLOW_WRITE	(1ULL << (PT_FIRST_AVAIL_BITS_SHIFT + 1))

 #define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)

@@ -1177,9 +1178,8 @@ static int kvm_set_pte_rmapp(struct kvm *kvm, unsigned long *rmapp,
 			new_spte = *sptep & ~PT64_BASE_ADDR_MASK;
 			new_spte |= (u64)new_pfn << PAGE_SHIFT;

-			new_spte &= ~PT_WRITABLE_MASK;
-			new_spte &= ~SPTE_HOST_WRITEABLE;
-			new_spte &= ~shadow_accessed_mask;
+			new_spte &= ~(PT_WRITABLE_MASK | SPTE_HOST_WRITEABLE |
+				      shadow_accessed_mask | SPTE_ALLOW_WRITE);

 			mmu_spte_clear_track_bits(sptep);
 			mmu_spte_set(sptep, new_spte);
@@ -2316,7 +2316,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 			goto done;
 		}

-		spte |= PT_WRITABLE_MASK;
+		spte |= PT_WRITABLE_MASK | SPTE_ALLOW_WRITE;

 		if (!vcpu->arch.mmu.direct_map
 		    && !(pte_access & ACC_WRITE_MASK)) {
@@ -2345,8 +2345,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 				 __func__, gfn);
 			ret = 1;
 			pte_access &= ~ACC_WRITE_MASK;
-			if (is_writable_pte(spte))
-				spte &= ~PT_WRITABLE_MASK;
+			spte &= ~PT_WRITABLE_MASK;
 		}
 	}

-- 
1.7.7.6