[PATCH v4 04/13] KVM: x86: Move n_memslots_pages recalc to kvm_arch_prepare_memory_region()

["Maciej S. Szmigiero" <mail@maciej.szmigiero.name>]

From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>

This allows us to return a proper error code in case we spot an underflow.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
---
 arch/x86/kvm/x86.c | 43 +++++++++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2ab0de7483ef..f39bf3c3a054 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11490,9 +11490,23 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				const struct kvm_userspace_memory_region *mem,
 				enum kvm_mr_change change)
 {
-	if (change == KVM_MR_CREATE || change == KVM_MR_MOVE)
-		return kvm_alloc_memslot_metadata(kvm, new,
-						  mem->memory_size >> PAGE_SHIFT);
+	if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) {
+		int ret;
+
+		ret = kvm_alloc_memslot_metadata(kvm, new,
+						 mem->memory_size >> PAGE_SHIFT);
+		if (ret)
+			return ret;
+
+		if (change == KVM_MR_CREATE)
+			kvm->arch.n_memslots_pages += new->npages;
+	} else if (change == KVM_MR_DELETE) {
+		if (WARN_ON(kvm->arch.n_memslots_pages < old->npages))
+			return -EIO;
+
+		kvm->arch.n_memslots_pages -= old->npages;
+	}
+
 	return 0;
 }
 
@@ -11589,22 +11603,15 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 				const struct kvm_memory_slot *new,
 				enum kvm_mr_change change)
 {
-	if (change == KVM_MR_CREATE || change == KVM_MR_DELETE) {
-		if (change == KVM_MR_CREATE)
-			kvm->arch.n_memslots_pages += new->npages;
-		else {
-			WARN_ON(kvm->arch.n_memslots_pages < old->npages);
-			kvm->arch.n_memslots_pages -= old->npages;
-		}
-
-		if (!kvm->arch.n_requested_mmu_pages) {
-			unsigned long nr_mmu_pages;
+	/* Only CREATE or DELETE affects n_memslots_pages */
+	if ((change == KVM_MR_CREATE || change == KVM_MR_DELETE) &&
+	    !kvm->arch.n_requested_mmu_pages) {
+		unsigned long nr_mmu_pages;
 
-			nr_mmu_pages = kvm->arch.n_memslots_pages *
-				KVM_PERMILLE_MMU_PAGES / 1000;
-			nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);
-			kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
-		}
+		nr_mmu_pages = kvm->arch.n_memslots_pages *
+			KVM_PERMILLE_MMU_PAGES / 1000;
+		nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);
+		kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
 	}
 
 	kvm_mmu_slot_apply_flags(kvm, old, new, change);