Re: [PATCH v8 36/46] KVM: selftests: Test that truncation does not change shared/private status

[Fuad Tabba]

On Fri, 19 Jun 2026 at 01:32, Ackerley Tng via B4 Relay
<devnull+ackerleytng.google.com@xxxxxxxxxx> wrote:
>
> From: Ackerley Tng <ackerleytng@xxxxxxxxxx>
>
> Add a test to verify that deallocating a page in a guest memfd region via
> fallocate() with FALLOC_FL_PUNCH_HOLE does not alter the shared or private
> status of the corresponding memory range.
>
> When a page backing a guest memfd mapping is deallocated, e.g., by punching
> a hole or truncating the file, and then subsequently faulted back in, the
> new page must inherit the correct shared/private status tracked by
> guest_memfd.
>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Co-developed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>

Cheers,
/fuad

> ---
>  .../selftests/kvm/x86/guest_memfd_conversions_test.c       | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c b/tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c
> index 0b024fb7227f0..f03af2c46426f 100644
> --- a/tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c
> +++ b/tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c
> @@ -10,6 +10,7 @@
>  #include <linux/sizes.h>
>
>  #include "kvm_util.h"
> +#include "kvm_syscalls.h"
>  #include "kselftest_harness.h"
>  #include "test_util.h"
>  #include "ucall_common.h"
> @@ -309,6 +310,19 @@ GMEM_CONVERSION_MULTIPAGE_TEST_INIT_SHARED(unallocated_folios, 8)
>                 test_convert_to_shared(t, i, 'B', 'C', 'D');
>  }
>
> +/* Truncation should not affect shared/private status. */
> +GMEM_CONVERSION_TEST_INIT_SHARED(truncate)
> +{
> +       host_do_rmw(t->mem, 0, 0, 'A');
> +       kvm_fallocate(t->gmem_fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE, 0, page_size);
> +       host_do_rmw(t->mem, 0, 0, 'A');
> +
> +       test_convert_to_private(t, 0, 'A', 'B');
> +
> +       kvm_fallocate(t->gmem_fd, FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE, 0, page_size);
> +       test_private(t, 0, 0, 'A');
> +}
> +
>  int main(int argc, char *argv[])
>  {
>         TEST_REQUIRE(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(KVM_X86_SW_PROTECTED_VM));
>
> --
> 2.55.0.rc0.738.g0c8ab3ebcc-goog
>
>