KVM: MMU: Fix dirty page setting for pages removed from rmap

Right now rmap_remove won't set the page as dirty if the shadow pte
pointed to this page had write access and then it became readonly.
This patches fixes that, by setting the page as dirty for spte changes from
write to readonly access.
Signed-off-by: NIzik Eidus <izike@qumranet.com>
Signed-off-by: NAvi Kivity <avi@qumranet.com>

arch/x86/kvm/mmu.c

@@ -890,6 +890,7 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
 {
 	u64 spte;
 	int was_rmapped = is_rmap_pte(*shadow_pte);
+	int was_writeble = is_writeble_pte(*shadow_pte);
 
 	pgprintk("%s: spte %llx access %x write_fault %d"
 		 " user_fault %d gfn %lx\n",
@@ -956,9 +957,12 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
 		rmap_add(vcpu, shadow_pte, gfn);
 		if (!is_rmap_pte(*shadow_pte))
 			kvm_release_page_clean(page);
-	}
+	} else {
+		if (was_writeble)
+			kvm_release_page_dirty(page);
 		else
 			kvm_release_page_clean(page);
+	}
 	if (!ptwrite || !*ptwrite)
 		vcpu->arch.last_pte_updated = shadow_pte;
 }