kvm: x86: mmu: Move pgtbl walk inside retry loop in fast_page_fault

Redo the page table walk in fast_page_fault when retrying so that we are
working on the latest PTE even if the hierarchy changes.
Signed-off-by: NJunaid Shahid <junaids@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -3088,14 +3088,16 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
 		return false;
 
 	walk_shadow_page_lockless_begin(vcpu);
-	for_each_shadow_entry_lockless(vcpu, gva, iterator, spte)
-		if (!is_shadow_present_pte(spte) || iterator.level < level)
-			break;
 
 	do {
 		bool remove_write_prot = false;
 		bool remove_acc_track;
 
+		for_each_shadow_entry_lockless(vcpu, gva, iterator, spte)
+			if (!is_shadow_present_pte(spte) ||
+			    iterator.level < level)
+				break;
+
 		sp = page_header(__pa(iterator.sptep));
 		if (!is_last_spte(spte, sp->role.level))
 			break;
@@ -3176,8 +3178,6 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level,
 			break;
 		}
 
-		spte = mmu_spte_get_lockless(iterator.sptep);
-
 	} while (true);
 
 	trace_fast_page_fault(vcpu, gva, error_code, iterator.sptep,