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	6432	guest_memfd range is not allowed (any number of memory regions can be bound to
6433	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
6436		−supports GUEST_MEMFD_FLAG_MMAP. Setting this flag on guest_memfd creation
6437		−enables mmap() and faulting of guest_memfd memory to host userspace.
	6435	+The capability KVM_CAP_GUEST_MEMFD_FLAGS enumerates the `flags` that can be
	6436	+specified via KVM_CREATE_GUEST_MEMFD. Currently defined flags:
	6437	+
	6438	+ ============================ ================================================
	6439	+ GUEST_MEMFD_FLAG_MMAP Enable using mmap() on the guest_memfd file
	6440	+ descriptor.
	6441	+ ============================ ================================================
6438	6442
6439	6443	When the KVM MMU performs a PFN lookup to service a guest fault and the backing
6440	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	962	#define KVM_CAP_ARM_EL2_E2H0 241
963	963	#define KVM_CAP_RISCV_MP_STATE_RESET 242
964	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	967	struct kvm_irq_routing_irqchip {
968	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	263	static void test_guest_memfd(unsigned long vm_type)
264	264	{
265		− uint64_t flags = 0;
266	265	struct kvm_vm *vm;
267	266	size_t total_size;
268	267	size_t page_size;
	268	+ uint64_t flags;
269	269	int fd;
270	270
271	271	page_size = getpagesize();
272	272	total_size = page_size * 4;
273	273
274	274	vm = vm_create_barebones_type(vm_type);
275		−
276		− if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP))
277		− flags \|= GUEST_MEMFD_FLAG_MMAP;
	275	+ flags = vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS);
278	276
279	277	test_create_guest_memfd_multiple(vm);
280	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	326	size_t size;
329	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	330	return;
333	331
334	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),
337		− "Default VM type should always support guest_memfd mmap()");
	334	+ TEST_ASSERT(vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_FLAGS) & GUEST_MEMFD_FLAG_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	338	size = vm->page_size;
340	339	fd = vm_create_guest_memfd(vm, size, GUEST_MEMFD_FLAG_MMAP);

virt/kvm/kvm_main.c+5−2

@@ -4928,8 +4928,11 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) · 4927 unmodified lines
4928	4928	#ifdef CONFIG_KVM_GUEST_MEMFD
4929	4929	case KVM_CAP_GUEST_MEMFD:
4930	4930	return 1;
4931		− case KVM_CAP_GUEST_MEMFD_MMAP:
4932		− return !kvm \|\| kvm_arch_supports_gmem_mmap(kvm);
	4931	+ case KVM_CAP_GUEST_MEMFD_FLAGS:
	4932	+ if (!kvm \|\| kvm_arch_supports_gmem_mmap(kvm))
	4933	+ return GUEST_MEMFD_FLAG_MMAP;
	4934	+
	4935	+ return 0;
4933	4936	#endif
4934	4937	default:
4935	4938	break;