KVM: MMU: remove prefault from invlpg handler

[Marcelo Tosatti <mtosatti@redhat.com>]

The invlpg prefault optimization breaks Windows 2008 R2 occasionally. 

The visible effect is that the invlpg handler instantiates a pte which
is, microseconds later, written with a different gfn by another vcpu.

The OS could have other mechanisms to prevent a present translation from 
being used, which the hypervisor is unaware of.

Fix by making invlpg emulation follow documented behaviour.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>


diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index a601713..58a0f1e 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -455,8 +455,6 @@ out_unlock:
 static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
 {
 	struct kvm_shadow_walk_iterator iterator;
-	pt_element_t gpte;
-	gpa_t pte_gpa = -1;
 	int level;
 	u64 *sptep;
 	int need_flush = 0;
@@ -470,10 +468,6 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
 		if (level == PT_PAGE_TABLE_LEVEL  ||
 		    ((level == PT_DIRECTORY_LEVEL && is_large_pte(*sptep))) ||
 		    ((level == PT_PDPE_LEVEL && is_large_pte(*sptep)))) {
-			struct kvm_mmu_page *sp = page_header(__pa(sptep));
-
-			pte_gpa = (sp->gfn << PAGE_SHIFT);
-			pte_gpa += (sptep - sp->spt) * sizeof(pt_element_t);
 
 			if (is_shadow_present_pte(*sptep)) {
 				rmap_remove(vcpu->kvm, sptep);
@@ -492,18 +486,6 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
 	if (need_flush)
 		kvm_flush_remote_tlbs(vcpu->kvm);
 	spin_unlock(&vcpu->kvm->mmu_lock);
-
-	if (pte_gpa == -1)
-		return;
-	if (kvm_read_guest_atomic(vcpu->kvm, pte_gpa, &gpte,
-				  sizeof(pt_element_t)))
-		return;
-	if (is_present_gpte(gpte) && (gpte & PT_ACCESSED_MASK)) {
-		if (mmu_topup_memory_caches(vcpu))
-			return;
-		kvm_mmu_pte_write(vcpu, pte_gpa, (const u8 *)&gpte,
-				  sizeof(pt_element_t), 0);
-	}
 }
 
 static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr)