KVM: x86/mmu: Add a field to control memslot rmap allocation

Add a field to control whether new memslots should have rmaps allocated for them. As of this change, it's not safe to skip allocating rmaps, so the field is always set to allocate rmaps. Future changes will make it safe to operate without rmaps, using the TDP MMU. Then further changes will allow the rmaps to be allocated lazily when needed for nested oprtation. No functional change expected. Reviewed-by: David Hildenbrand <[email protected]> Signed-off-by: Ben Gardon <[email protected]> Message-Id: <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
ashr · Jun 17, 2021 · a255740 · a255740
1 parent b10a038
commit a255740
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Showing 3 changed files with 16 additions and 5 deletions.
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
@@ -1124,6 +1124,12 @@ struct kvm_arch {
 	 */
 	spinlock_t tdp_mmu_pages_lock;
 #endif /* CONFIG_X86_64 */
+
+	/*
+	 * If set, rmaps have been allocated for all memslots and should be
+	 * allocated for any newly created or modified memslots.
+	 */
+	bool memslots_have_rmaps;
 };
 
 struct kvm_vm_stat {

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
@@ -5511,6 +5511,8 @@ void kvm_mmu_init_vm(struct kvm *kvm)
 
 	kvm_mmu_init_tdp_mmu(kvm);
 
+	kvm->arch.memslots_have_rmaps = true;
+
 	node->track_write = kvm_mmu_pte_write;
 	node->track_flush_slot = kvm_mmu_invalidate_zap_pages_in_memslot;
 	kvm_page_track_register_notifier(kvm, node);

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
@@ -10962,7 +10962,8 @@ static int memslot_rmap_alloc(struct kvm_memory_slot *slot,
 	return 0;
 }
 
-static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
+static int kvm_alloc_memslot_metadata(struct kvm *kvm,
+				      struct kvm_memory_slot *slot,
 				      unsigned long npages)
 {
 	int i, r;
@@ -10974,9 +10975,11 @@ static int kvm_alloc_memslot_metadata(struct kvm_memory_slot *slot,
 	 */
 	memset(&slot->arch, 0, sizeof(slot->arch));
 
-	r = memslot_rmap_alloc(slot, npages);
-	if (r)
-		return r;
+	if (kvm->arch.memslots_have_rmaps) {
+		r = memslot_rmap_alloc(slot, npages);
+		if (r)
+			return r;
+	}
 
 	for (i = 1; i < KVM_NR_PAGE_SIZES; ++i) {
 		struct kvm_lpage_info *linfo;
@@ -11047,7 +11050,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				enum kvm_mr_change change)
 {
 	if (change == KVM_MR_CREATE || change == KVM_MR_MOVE)
-		return kvm_alloc_memslot_metadata(memslot,
+		return kvm_alloc_memslot_metadata(kvm, memslot,
 						  mem->memory_size >> PAGE_SHIFT);
 	return 0;
 }