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

[Fuad Tabba <tabba@google.com>]

Hi Gavin,

On Wed, 4 Jun 2025 at 10:20, Gavin Shan <gshan@redhat.com> wrote:
>
> Hi Fuad,
>
> 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.

> # ./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!
/fuad

> > +     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
>