Re: [PATCH v9 16/17] KVM: selftests: guest_memfd mmap() test when mapping is allowed

[Gavin Shan <gshan@redhat.com>]

Hi Fuad,

On 5/14/25 2:34 AM, Fuad Tabba wrote:
> Expand the guest_memfd selftests to include testing mapping guest
> memory for VM types that support it.
> 
> Also, build the guest_memfd selftest for arm64.
> 
> Co-developed-by: Ackerley Tng <ackerleytng@google.com>
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> Signed-off-by: Fuad Tabba <tabba@google.com>
> ---
>   tools/testing/selftests/kvm/Makefile.kvm      |   1 +
>   .../testing/selftests/kvm/guest_memfd_test.c  | 145 +++++++++++++++---
>   2 files changed, 126 insertions(+), 20 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
> index f62b0a5aba35..ccf95ed037c3 100644
> --- a/tools/testing/selftests/kvm/Makefile.kvm
> +++ b/tools/testing/selftests/kvm/Makefile.kvm
> @@ -163,6 +163,7 @@ TEST_GEN_PROGS_arm64 += access_tracking_perf_test
>   TEST_GEN_PROGS_arm64 += arch_timer
>   TEST_GEN_PROGS_arm64 += coalesced_io_test
>   TEST_GEN_PROGS_arm64 += dirty_log_perf_test
> +TEST_GEN_PROGS_arm64 += guest_memfd_test
>   TEST_GEN_PROGS_arm64 += get-reg-list
>   TEST_GEN_PROGS_arm64 += memslot_modification_stress_test
>   TEST_GEN_PROGS_arm64 += memslot_perf_test
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index ce687f8d248f..443c49185543 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -34,12 +34,46 @@ static void test_file_read_write(int fd)
>   		    "pwrite on a guest_mem fd should fail");
>   }
>   
> -static void test_mmap(int fd, size_t page_size)
> +static void test_mmap_allowed(int fd, size_t page_size, size_t total_size)
> +{
> +	const char val = 0xaa;
> +	char *mem;
> +	size_t i;
> +	int ret;
> +
> +	mem = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> +	TEST_ASSERT(mem != MAP_FAILED, "mmaping() guest memory should pass.");
> +
> +	memset(mem, val, total_size);
> +	for (i = 0; i < total_size; i++)
> +		TEST_ASSERT_EQ(mem[i], val);
> +
> +	ret = fallocate(fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE, 0,
> +			page_size);
> +	TEST_ASSERT(!ret, "fallocate the first page should succeed");
> +
> +	for (i = 0; i < page_size; i++)
> +		TEST_ASSERT_EQ(mem[i], 0x00);
> +	for (; i < total_size; i++)
> +		TEST_ASSERT_EQ(mem[i], val);
> +
> +	memset(mem, val, total_size);
> +	for (i = 0; i < total_size; i++)
> +		TEST_ASSERT_EQ(mem[i], val);
> +

The last memset() and check the resident values look redudant because same
test has been covered by the first memset(). If we really want to double
confirm that the page-cache is writabble, it would be enough to cover the
first page. Otherwise, I guess this hunk of code can be removed :)

	memset(mem, val, page_size);
	for (i = 0; i < page_size; i++)
		TEST_ASSERT_EQ(mem[i], val);

> +	ret = munmap(mem, total_size);
> +	TEST_ASSERT(!ret, "munmap should succeed");
> +}
> +
> +static void test_mmap_denied(int fd, size_t page_size, size_t total_size)
>   {
>   	char *mem;
>   
>   	mem = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
>   	TEST_ASSERT_EQ(mem, MAP_FAILED);
> +
> +	mem = mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> +	TEST_ASSERT_EQ(mem, MAP_FAILED);
>   }
>   
>   static void test_file_size(int fd, size_t page_size, size_t total_size)
> @@ -120,26 +154,19 @@ static void test_invalid_punch_hole(int fd, size_t page_size, size_t total_size)
>   	}
>   }
>   
> -static void test_create_guest_memfd_invalid(struct kvm_vm *vm)
> +static void test_create_guest_memfd_invalid_sizes(struct kvm_vm *vm,
> +						  uint64_t guest_memfd_flags,
> +						  size_t page_size)
>   {
> -	size_t page_size = getpagesize();
> -	uint64_t flag;
>   	size_t size;
>   	int fd;
>   
>   	for (size = 1; size < page_size; size++) {
> -		fd = __vm_create_guest_memfd(vm, size, 0);
> +		fd = __vm_create_guest_memfd(vm, size, guest_memfd_flags);
>   		TEST_ASSERT(fd == -1 && errno == EINVAL,
>   			    "guest_memfd() with non-page-aligned page size '0x%lx' should fail with EINVAL",
>   			    size);
>   	}
> -
> -	for (flag = BIT(0); flag; flag <<= 1) {
> -		fd = __vm_create_guest_memfd(vm, page_size, flag);
> -		TEST_ASSERT(fd == -1 && errno == EINVAL,
> -			    "guest_memfd() with flag '0x%lx' should fail with EINVAL",
> -			    flag);
> -	}
>   }
>   
>   static void test_create_guest_memfd_multiple(struct kvm_vm *vm)
> @@ -170,30 +197,108 @@ static void test_create_guest_memfd_multiple(struct kvm_vm *vm)
>   	close(fd1);
>   }
>   
> -int main(int argc, char *argv[])
> +static void test_with_type(unsigned long vm_type, uint64_t guest_memfd_flags,
> +			   bool expect_mmap_allowed)
>   {
> -	size_t page_size;
> +	struct kvm_vm *vm;
>   	size_t total_size;
> +	size_t page_size;
>   	int fd;
> -	struct kvm_vm *vm;
>   
> -	TEST_REQUIRE(kvm_has_cap(KVM_CAP_GUEST_MEMFD));
> +	if (!(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(vm_type)))
> +		return;
>   

The check seems incorrect for aarch64 since 0 is always returned from
kvm_check_cap() there. The test is skipped for VM_TYPE_DEFAULT on aarch64.
So it would be something like below:

	#define VM_TYPE_DEFAULT		0

	if (vm_type != VM_TYPE_DEFAULT &&
	    !(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(vm_type)))
		return;

>   	page_size = getpagesize();
>   	total_size = page_size * 4;
>   
> -	vm = vm_create_barebones();
> +	vm = vm_create_barebones_type(vm_type);
>   
> -	test_create_guest_memfd_invalid(vm);
>   	test_create_guest_memfd_multiple(vm);
> +	test_create_guest_memfd_invalid_sizes(vm, guest_memfd_flags, page_size);
>   
> -	fd = vm_create_guest_memfd(vm, total_size, 0);
> +	fd = vm_create_guest_memfd(vm, total_size, guest_memfd_flags);
>   
>   	test_file_read_write(fd);
> -	test_mmap(fd, page_size);
> +
> +	if (expect_mmap_allowed)
> +		test_mmap_allowed(fd, page_size, total_size);
> +	else
> +		test_mmap_denied(fd, page_size, total_size);
> +
>   	test_file_size(fd, page_size, total_size);
>   	test_fallocate(fd, page_size, total_size);
>   	test_invalid_punch_hole(fd, page_size, total_size);
>   
>   	close(fd);
> +	kvm_vm_release(vm);
> +}
> +
> +static void test_vm_type_gmem_flag_validity(unsigned long vm_type,
> +					    uint64_t expected_valid_flags)
> +{
> +	size_t page_size = getpagesize();
> +	struct kvm_vm *vm;
> +	uint64_t flag = 0;
> +	int fd;
> +
> +	if (!(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(vm_type)))
> +		return;

Same as above

> +
> +	vm = vm_create_barebones_type(vm_type);
> +
> +	for (flag = BIT(0); flag; flag <<= 1) {
> +		fd = __vm_create_guest_memfd(vm, page_size, flag);
> +
> +		if (flag & expected_valid_flags) {
> +			TEST_ASSERT(fd > 0,
> +				    "guest_memfd() with flag '0x%lx' should be valid",
> +				    flag);
> +			close(fd);
> +		} else {
> +			TEST_ASSERT(fd == -1 && errno == EINVAL,
> +				    "guest_memfd() with flag '0x%lx' should fail with EINVAL",
> +				    flag);

It's more robust to have:

			TEST_ASSERT(fd < 0 && errno == EINVAL, ...);

> +		}
> +	}
> +
> +	kvm_vm_release(vm);
> +}
> +
> +static void test_gmem_flag_validity(void)
> +{
> +	uint64_t non_coco_vm_valid_flags = 0;
> +
> +	if (kvm_has_cap(KVM_CAP_GMEM_SHARED_MEM))
> +		non_coco_vm_valid_flags = GUEST_MEMFD_FLAG_SUPPORT_SHARED;
> +
> +	test_vm_type_gmem_flag_validity(VM_TYPE_DEFAULT, non_coco_vm_valid_flags);
> +
> +#ifdef __x86_64__
> +	test_vm_type_gmem_flag_validity(KVM_X86_SW_PROTECTED_VM, non_coco_vm_valid_flags);
> +	test_vm_type_gmem_flag_validity(KVM_X86_SEV_VM, 0);
> +	test_vm_type_gmem_flag_validity(KVM_X86_SEV_ES_VM, 0);
> +	test_vm_type_gmem_flag_validity(KVM_X86_SNP_VM, 0);
> +	test_vm_type_gmem_flag_validity(KVM_X86_TDX_VM, 0);
> +#endif
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	TEST_REQUIRE(kvm_has_cap(KVM_CAP_GUEST_MEMFD));
> +
> +	test_gmem_flag_validity();
> +
> +	test_with_type(VM_TYPE_DEFAULT, 0, false);
> +	if (kvm_has_cap(KVM_CAP_GMEM_SHARED_MEM)) {
> +		test_with_type(VM_TYPE_DEFAULT, GUEST_MEMFD_FLAG_SUPPORT_SHARED,
> +			       true);
> +	}
> +
> +#ifdef __x86_64__
> +	test_with_type(KVM_X86_SW_PROTECTED_VM, 0, false);
> +	if (kvm_has_cap(KVM_CAP_GMEM_SHARED_MEM)) {
> +		test_with_type(KVM_X86_SW_PROTECTED_VM,
> +			       GUEST_MEMFD_FLAG_SUPPORT_SHARED, true);
> +	}
> +#endif
>   }

Thanks,
Gavin