Re: [PATCH v10 16/16] KVM: selftests: guest_memfd mmap() test when mapping is allowed

[Gavin Shan <gshan@redhat.com>]

Hi Fuad,

On 6/4/25 7:48 PM, Fuad Tabba wrote:
> On Wed, 4 Jun 2025 at 10:20, Gavin Shan <gshan@redhat.com> wrote:
>>
>> On 5/28/25 4:02 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  | 162 +++++++++++++++---
>>>    2 files changed, 142 insertions(+), 21 deletions(-)
>>>
>>
>> The test case fails on 64KB host, and the file size in test_create_guest_memfd_multiple()
>> would be page_size and (2 * page_size). The fixed size 4096 and 8192 aren't aligned to 64KB.
> 
> Yes, however, this patch didn't introduce or modify this test. I think
> it's better to fix it in a separate patch independent of this series.
> 

Yeah, it can be separate patch or a preparatory patch before PATCH[16/16]
of this series because x86 hasn't 64KB page size. The currently fixed sizes
(4096 and 8192) are aligned to page size on x86. and 'guest-memfd-test' is
enabled on arm64 by this series.

>> # ./guest_memfd_test
>> Random seed: 0x6b8b4567
>> ==== Test Assertion Failure ====
>>     guest_memfd_test.c:178: fd1 != -1
>>     pid=7565 tid=7565 errno=22 - Invalid argument
>>        1 0x000000000040252f: test_create_guest_memfd_multiple at guest_memfd_test.c:178
>>        2  (inlined by) test_with_type at guest_memfd_test.c:231
>>        3 0x00000000004020c7: main at guest_memfd_test.c:306
>>        4 0x0000ffff8cec733f: ?? ??:0
>>        5 0x0000ffff8cec7417: ?? ??:0
>>        6 0x00000000004021ef: _start at ??:?
>>     memfd creation should succeed
>>
>>> 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..3d6765bc1f28 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.");
>>> +
>>
>> If you agree, I think it would be nice to ensure guest-memfd doesn't support
>> copy-on-write, more details are provided below.
> 
> Good idea. I think we can do this without adding much more code. I'll
> add a check in test_mmap_allowed(), since the idea is, even if mmap()
> is supported, we still can't COW. I'll rename the functions to make
> this a bit clearer (i.e., supported instead of allowed).
> 
> Thank you for this and thank you for the reviews!
> 

Sounds good to me  :)

> 
>>> +     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, page_size);
>>> +     for (i = 0; i < total_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);
>>>    }
>>
>> Add one more argument to test_mmap_denied as the flags passed to mmap().
>>
>> static void test_mmap_denied(int fd, size_t page_size, size_t total_size, int mmap_flags)
>> {
>>          mem = mmap(NULL, total_size, PROT_READ | PROT_WRITE, mmap_flags, fd, 0);
>> }
>>
>>>
>>>    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);
>>> -             TEST_ASSERT(fd == -1 && errno == EINVAL,
>>> +             fd = __vm_create_guest_memfd(vm, size, guest_memfd_flags);
>>> +             TEST_ASSERT(fd < 0 && 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 +197,123 @@ static void test_create_guest_memfd_multiple(struct kvm_vm *vm)
>>>        close(fd1);
>>>    }
>>>
>>> -int main(int argc, char *argv[])
>>> +#define GUEST_MEMFD_TEST_SLOT 10
>>> +#define GUEST_MEMFD_TEST_GPA 0x100000000
>>> +
>>> +static bool check_vm_type(unsigned long vm_type)
>>>    {
>>> -     size_t page_size;
>>> +     /*
>>> +      * Not all architectures support KVM_CAP_VM_TYPES. However, those that
>>> +      * support guest_memfd have that support for the default VM type.
>>> +      */
>>> +     if (vm_type == VM_TYPE_DEFAULT)
>>> +             return true;
>>> +
>>> +     return kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(vm_type);
>>> +}
>>> +
>>> +static void test_with_type(unsigned long vm_type, uint64_t guest_memfd_flags,
>>> +                        bool expect_mmap_allowed)
>>> +{
>>> +     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 (!check_vm_type(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);
>>> +
>>
>>          if (expect_mmap_allowed) {
>>                  test_mmap_denied(fd, page_size, total_size, MAP_PRIVATE);
>>                  test_mmap_allowed(fd, page_size, total_size);
>>          } else {
>>                  test_mmap_denied(fd, page_size, total_size, MAP_SHARED);
>>          }
>>
>>>        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 (!check_vm_type(vm_type))
>>> +             return;
>>> +
>>> +     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 < 0 && errno == EINVAL,
>>> +                                 "guest_memfd() with flag '0x%lx' should fail with EINVAL",
>>> +                                 flag);
>>> +             }
>>> +     }
>>> +
>>> +     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