KVM: Recalculate mmu pages needed for every memory region change

Instead of incrementally changing the mmu cache size for every memory slot
operation, recalculate it from scratch.  This is simpler and safer.
Signed-off-by: Zhang Xiantao <xiantao.zhang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

drivers/kvm/kvm_main.c

@@ -333,26 +333,13 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (mem->slot >= kvm->nmemslots)
 		kvm->nmemslots = mem->slot + 1;
 
+	*memslot = new;
+
 	if (!kvm->n_requested_mmu_pages) {
-		unsigned int n_pages;
-
-		if (npages) {
-			n_pages = npages * KVM_PERMILLE_MMU_PAGES / 1000;
-			kvm_mmu_change_mmu_pages(kvm, kvm->n_alloc_mmu_pages +
-						 n_pages);
-		} else {
-			unsigned int nr_mmu_pages;
-
-			n_pages = old.npages * KVM_PERMILLE_MMU_PAGES / 1000;
-			nr_mmu_pages = kvm->n_alloc_mmu_pages - n_pages;
-			nr_mmu_pages = max(nr_mmu_pages,
-				        (unsigned int) KVM_MIN_ALLOC_MMU_PAGES);
-			kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
-		}
+		unsigned int nr_mmu_pages = kvm_mmu_calculate_mmu_pages(kvm);
+		kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
 	}
 
-	*memslot = new;
-
 	kvm_mmu_slot_remove_write_access(kvm, mem->slot);
 	kvm_flush_remote_tlbs(kvm);
 

drivers/kvm/mmu.c

@@ -1535,6 +1535,25 @@ int kvm_mmu_module_init(void)
 	return -ENOMEM;
 }
 
+/*
+ * Caculate mmu pages needed for kvm.
+ */
+unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm)
+{
+	int i;
+	unsigned int nr_mmu_pages;
+	unsigned int  nr_pages = 0;
+
+	for (i = 0; i < kvm->nmemslots; i++)
+		nr_pages += kvm->memslots[i].npages;
+
+	nr_mmu_pages = nr_pages * KVM_PERMILLE_MMU_PAGES / 1000;
+	nr_mmu_pages = max(nr_mmu_pages,
+			(unsigned int) KVM_MIN_ALLOC_MMU_PAGES);
+
+	return nr_mmu_pages;
+}
+
 #ifdef AUDIT
 
 static const char *audit_msg;

drivers/kvm/x86.h

@@ -236,6 +236,7 @@ void kvm_mmu_set_nonpresent_ptes(u64 trap_pte, u64 notrap_pte);
 int kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
 void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
 void kvm_mmu_zap_all(struct kvm *kvm);
+unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
 void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages);
 
 enum emulation_result {