Revert "KVM: MMU: lazily drop large spte"

This reverts commit caf6900f2d8aaebe404c976753f6813ccd31d95e.

It is causing migration failures, reference
https://bugzilla.kernel.org/show_bug.cgi?id=54061.

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

arch/x86/kvm/mmu.c

@@ -1105,7 +1105,8 @@ static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
 
 /*
  * Write-protect on the specified @sptep, @pt_protect indicates whether
- * spte write-protection is caused by protecting shadow page table.
+ * spte writ-protection is caused by protecting shadow page table.
+ * @flush indicates whether tlb need be flushed.
  *
  * Note: write protection is difference between drity logging and spte
  * protection:
@@ -1114,9 +1115,10 @@ static void drop_large_spte(struct kvm_vcpu *vcpu, u64 *sptep)
  * - for spte protection, the spte can be writable only after unsync-ing
  *   shadow page.
  *
- * Return true if tlb need be flushed.
+ * Return true if the spte is dropped.
  */
-static bool spte_write_protect(struct kvm *kvm, u64 *sptep, bool pt_protect)
+static bool
+spte_write_protect(struct kvm *kvm, u64 *sptep, bool *flush, bool pt_protect)
 {
 	u64 spte = *sptep;
 
@@ -1126,11 +1128,17 @@ static bool spte_write_protect(struct kvm *kvm, u64 *sptep, bool pt_protect)
 
 	rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep);
 
+	if (__drop_large_spte(kvm, sptep)) {
+		*flush |= true;
+		return true;
+	}
+
 	if (pt_protect)
 		spte &= ~SPTE_MMU_WRITEABLE;
 	spte = spte & ~PT_WRITABLE_MASK;
 
-	return mmu_spte_update(sptep, spte);
+	*flush |= mmu_spte_update(sptep, spte);
+	return false;
 }
 
 static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp,
@@ -1142,8 +1150,11 @@ static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp,
 
 	for (sptep = rmap_get_first(*rmapp, &iter); sptep;) {
 		BUG_ON(!(*sptep & PT_PRESENT_MASK));
+		if (spte_write_protect(kvm, sptep, &flush, pt_protect)) {
+			sptep = rmap_get_first(*rmapp, &iter);
+			continue;
+		}
 
-		flush |= spte_write_protect(kvm, sptep, pt_protect);
 		sptep = rmap_get_next(&iter);
 	}
 
@@ -2581,8 +2592,6 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t v, int write,
 			break;
 		}
 
-		drop_large_spte(vcpu, iterator.sptep);
-
 		if (!is_shadow_present_pte(*iterator.sptep)) {
 			u64 base_addr = iterator.addr;