linux-kernel - Re: [PATCH 4/6] KVM: selftests: Add test coverage for guest_memfd without GUEST_MEMFD_FLAG

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Message-ID: <CA+EHjTzntT9idx56RB8XuD+5Ja=3jmfNRiqfh79aQqm0kzNDrA@mail.gmail.com>
Date: Mon, 29 Sep 2025 10:24:21 +0100
From: Fuad Tabba <tabba@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, 
	Janosch Frank <frankja@...ux.ibm.com>, Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, David Hildenbrand <david@...hat.com>, 
	Ackerley Tng <ackerleytng@...gle.com>
Subject: Re: [PATCH 4/6] KVM: selftests: Add test coverage for guest_memfd
 without GUEST_MEMFD_FLAG_MMAP

On Fri, 26 Sept 2025 at 17:31, Sean Christopherson <seanjc@...gle.com> wrote:
>
> From: Ackerley Tng <ackerleytng@...gle.com>
>
> If a VM type supports KVM_CAP_GUEST_MEMFD_MMAP, the guest_memfd test will
> run all test cases with GUEST_MEMFD_FLAG_MMAP set.  This leaves the code
> path for creating a non-mmap()-able guest_memfd on a VM that supports
> mappable guest memfds untested.
>
> Refactor the test to run the main test suite with a given set of flags.
> Then, for VM types that support the mappable capability, invoke the test
> suite twice: once with no flags, and once with GUEST_MEMFD_FLAG_MMAP
> set.
>
> This ensures both creation paths are properly exercised on capable VMs.
>
> test_guest_memfd_flags() tests valid flags, hence it can be run just once
> per VM type, and valid flag identification can be moved into the test
> function.
>
> Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
> [sean: use double-underscores for the inner helper]
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Fuad Tabba <tabba@...gle.com>
Tested-by: Fuad Tabba <tabba@...gle.com>

Cheers,
/fuad



> ---
>  .../testing/selftests/kvm/guest_memfd_test.c  | 30 ++++++++++++-------
>  1 file changed, 19 insertions(+), 11 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index 60c6dec63490..5a50a28ce1fa 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -239,11 +239,16 @@ static void test_create_guest_memfd_multiple(struct kvm_vm *vm)
>         close(fd1);
>  }
>
> -static void test_guest_memfd_flags(struct kvm_vm *vm, uint64_t valid_flags)
> +static void test_guest_memfd_flags(struct kvm_vm *vm)
>  {
> +       uint64_t valid_flags = 0;
>         uint64_t flag;
>         int fd;
>
> +       if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP))
> +               valid_flags |= GUEST_MEMFD_FLAG_MMAP |
> +                              GUEST_MEMFD_FLAG_DEFAULT_SHARED;
> +
>         for (flag = BIT(0); flag; flag <<= 1) {
>                 fd = __vm_create_guest_memfd(vm, page_size, flag);
>                 if (flag & valid_flags) {
> @@ -267,16 +272,8 @@ do {                                                                       \
>         close(fd);                                                      \
>  } while (0)
>
> -static void test_guest_memfd(unsigned long vm_type)
> +static void __test_guest_memfd(struct kvm_vm *vm, uint64_t flags)
>  {
> -       uint64_t flags = 0;
> -       struct kvm_vm *vm;
> -
> -       vm = vm_create_barebones_type(vm_type);
> -
> -       if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP))
> -               flags |= GUEST_MEMFD_FLAG_MMAP | GUEST_MEMFD_FLAG_DEFAULT_SHARED;
> -
>         test_create_guest_memfd_multiple(vm);
>         test_create_guest_memfd_invalid_sizes(vm, flags);
>
> @@ -292,8 +289,19 @@ static void test_guest_memfd(unsigned long vm_type)
>         gmem_test(file_size, vm, flags);
>         gmem_test(fallocate, vm, flags);
>         gmem_test(invalid_punch_hole, vm, flags);
> +}
>
> -       test_guest_memfd_flags(vm, flags);
> +static void test_guest_memfd(unsigned long vm_type)
> +{
> +       struct kvm_vm *vm = vm_create_barebones_type(vm_type);
> +
> +       test_guest_memfd_flags(vm);
> +
> +       __test_guest_memfd(vm, 0);
> +
> +       if (vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP))
> +               __test_guest_memfd(vm, GUEST_MEMFD_FLAG_MMAP |
> +                                      GUEST_MEMFD_FLAG_DEFAULT_SHARED);
>
>         kvm_vm_free(vm);
>  }
> --
> 2.51.0.536.g15c5d4f767-goog
>