KVM: Rework KVM_CAP_GUEST_MEMFD_MMAP into KVM_CAP_GUEST_MEMFD_FLAGS

Rework the not-yet-released KVM_CAP_GUEST_MEMFD_MMAP into a more generic KVM_CAP_GUEST_MEMFD_FLAGS capability so that adding new flags doesn't require a new capability, and so that developers aren't tempted to bundle multiple flags into a single capability. Note, kvm_vm_ioctl_check_extension_generic() can only return a 32-bit value, but that limitation can be easily circumvented by adding e.g. KVM_CAP_GUEST_MEMFD_FLAGS2 in the unlikely event guest_memfd supports more than 32 flags.

Sean Christopherson committed 1 year ago

Commit d2042d81 parent 034417c4 files · +19 −13Browse files

Unified · Split

4 files

Documentation/virt/kvm/api.rst +7 −3
include/uapi/linux/kvm.h +1 −1
tools/testing/selftests/kvm/guest_memfd_test.c +6 −7
virt/kvm/kvm_main.c +5 −2

Documentation/virt/kvm/api.rst+7−3

@@ -6432,9 +6432,13 @@ most one mapping per page, i.e. binding multiple memory regions to a single · 6431 unmodified lines
6432	guest_memfd range is not allowed (any number of memory regions can be bound to	6432	guest_memfd range is not allowed (any number of memory regions can be bound to
6433	a single guest_memfd file, but the bound ranges must not overlap).	6433	a single guest_memfd file, but the bound ranges must not overlap).
6434		6434
6435	When the capability KVM_CAP_GUEST_MEMFD_MMAP is supported, the 'flags' field	6435	The capability KVM_CAP_GUEST_MEMFD_FLAGS enumerates the `flags` that can be
6436	supports GUEST_MEMFD_FLAG_MMAP. Setting this flag on guest_memfd creation	6436	specified via KVM_CREATE_GUEST_MEMFD. Currently defined flags:
6437	enables mmap() and faulting of guest_memfd memory to host userspace.	6437
		6438	============================ ================================================
		6439	GUEST_MEMFD_FLAG_MMAP Enable using mmap() on the guest_memfd file
		6440	descriptor.
		6441	============================ ================================================
6438		6442
6439	When the KVM MMU performs a PFN lookup to service a guest fault and the backing	6443	When the KVM MMU performs a PFN lookup to service a guest fault and the backing
6440	guest_memfd has the GUEST_MEMFD_FLAG_MMAP set, then the fault will always be	6444	guest_memfd has the GUEST_MEMFD_FLAG_MMAP set, then the fault will always be

include/uapi/linux/kvm.h+1−1

@@ -962,7 +962,7 @@ struct kvm_enable_cap { · 961 unmodified lines
962	#define KVM_CAP_ARM_EL2_E2H0 241	962	#define KVM_CAP_ARM_EL2_E2H0 241
963	#define KVM_CAP_RISCV_MP_STATE_RESET 242	963	#define KVM_CAP_RISCV_MP_STATE_RESET 242
964	#define KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED 243	964	#define KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED 243
965	#define KVM_CAP_GUEST_MEMFD_MMAP 244	965	#define KVM_CAP_GUEST_MEMFD_FLAGS 244
966		966
967	struct kvm_irq_routing_irqchip {	967	struct kvm_irq_routing_irqchip {
968	__u32 irqchip;	968	__u32 irqchip;

tools/testing/selftests/kvm/guest_memfd_test.c+6−7

@@ -262,19 +262,17 @@ static void test_guest_memfd_flags(struct kvm_vm *vm, uint64_t valid_flags) · 261 unmodified lines
262		262
263	static void test_guest_memfd(unsigned long vm_type)	263	static void test_guest_memfd(unsigned long vm_type)
264	{	264	{
265	uint64_t flags = 0;
266	struct kvm_vm *vm;	265	struct kvm_vm *vm;
267	size_t total_size;	266	size_t total_size;
268	size_t page_size;	267	size_t page_size;
		268	uint64_t flags;
269	int fd;	269	int fd;
270		270
271	page_size = getpagesize();	271	page_size = getpagesize();
272	total_size = page_size * 4;	272	total_size = page_size * 4;
273		273
274	vm = vm_create_barebones_type(vm_type);	274	vm = vm_create_barebones_type(vm_type);
275		275	flags = vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS);
276	if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP))
277	flags \|= GUEST_MEMFD_FLAG_MMAP;
278		276
279	test_create_guest_memfd_multiple(vm);	277	test_create_guest_memfd_multiple(vm);
280	test_create_guest_memfd_invalid_sizes(vm, flags, page_size);	278	test_create_guest_memfd_invalid_sizes(vm, flags, page_size);
@@ -328,13 +326,14 @@ static void test_guest_memfd_guest(void) · 47 unmodified lines
328	size_t size;	326	size_t size;
329	int fd, i;	327	int fd, i;
330		328
331	if (!kvm_has_cap(KVM_CAP_GUEST_MEMFD_MMAP))	329	if (!kvm_check_cap(KVM_CAP_GUEST_MEMFD_FLAGS))
332	return;	330	return;
333		331
334	vm = __vm_create_shape_with_one_vcpu(VM_SHAPE_DEFAULT, &vcpu, 1, guest_code);	332	vm = __vm_create_shape_with_one_vcpu(VM_SHAPE_DEFAULT, &vcpu, 1, guest_code);
335		333
336	TEST_ASSERT(vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP),	334	TEST_ASSERT(vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS) & GUEST_MEMFD_FLAG_MMAP,
337	"Default VM type should always support guest_memfd mmap()");	335	"Default VM type should support MMAP, supported flags = 0x%x",
		336	vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS));
338		337
339	size = vm->page_size;	338	size = vm->page_size;
340	fd = vm_create_guest_memfd(vm, size, GUEST_MEMFD_FLAG_MMAP);	339	fd = vm_create_guest_memfd(vm, size, GUEST_MEMFD_FLAG_MMAP);

virt/kvm/kvm_main.c+5−2

 #ifdef CONFIG_KVM_GUEST_MEMFD
 	case KVM_CAP_GUEST_MEMFD:
 		return 1;
-	case KVM_CAP_GUEST_MEMFD_MMAP:
+	case KVM_CAP_GUEST_MEMFD_FLAGS:
-		return !kvm || kvm_arch_supports_gmem_mmap(kvm);
+		if (!kvm || kvm_arch_supports_gmem_mmap(kvm))
+			return GUEST_MEMFD_FLAG_MMAP;
+		return 0;
 #endif
 	default:
 		break;