Re: [PATCH RFC 10/17] KVM: selftests: Test rejection of hugepage tmpfs mounts

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] kvm: selftests: test_resource_fd_tmpfs_huge aborts on systems without THP
--

commit 3b3c9f0d1e79074e146192602be76f64b250554b
Author: Ackerley Tng <ackerleytng@google.com>

    KVM: selftests: Test rejection of hugepage tmpfs mounts

This commit adds a test to verify that guest_memfd creation fails when backed
by a tmpfs mount with huge pages enabled.

> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index 5d017164d7b45..e8199ed17b0f8 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -526,6 +526,21 @@ static void test_resource_fd_tmpfs_swap(struct kvm_vm *vm)
>  	close(pool_fd);
>  }
>  
> +static void test_resource_fd_tmpfs_huge(struct kvm_vm *vm)
> +{
> +	int pool_fd, fd;
> +
> +	pool_fd = create_tmpfs_pool_fd("always", true, page_size);

[Severity: Medium]
Will this unconditionally abort the test suite on systems that lack
Transparent Huge Pages (THP) support?

When create_tmpfs_pool_fd() is called, it issues an fsconfig syscall wrapped
in a hard assertion:

tools/testing/selftests/kvm/guest_memfd_test.c:create_tmpfs_pool_fd() {
	...
	if (huge)
		TEST_ASSERT(!syscall(__NR_fsconfig, fs_fd, FSCONFIG_SET_STRING,
				     "huge", huge, 0), "fsconfig huge failed");
	...
}

If the host kernel was built without CONFIG_TRANSPARENT_HUGEPAGE or otherwise
lacks hardware THP support, wouldn't the fsconfig syscall fail with -EINVAL
and trigger the hard assert, aborting the rest of the guest_memfd_test suite?

> +
> +	fd = __vm_create_guest_memfd_resource(vm, page_size,
> +					      GUEST_MEMFD_FLAG_USE_RESOURCE,
> +					      pool_fd);
> +	TEST_ASSERT(fd < 0, "guest_memfd with huge-enabled tmpfs should fail");
> +	TEST_ASSERT_EQ(errno, EINVAL);
> +
> +	close(pool_fd);
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260925-gmem-tmpfs-backend-v1-0-d36159822d18@google.com?part=10