linux-kernel - Re: [RFC PATCH v2 03/51] KVM: selftests: Update guest_memfd_test for INIT

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Message-ID: <6825f0f3ac8a7_337c392942d@iweiny-mobl.notmuch>
Date: Thu, 15 May 2025 08:49:39 -0500
From: Ira Weiny <ira.weiny@...el.com>
To: Ackerley Tng <ackerleytng@...gle.com>, <kvm@...r.kernel.org>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	<linux-fsdevel@...r.kernel.org>
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Subject: Re: [RFC PATCH v2 03/51] KVM: selftests: Update guest_memfd_test for
 INIT_PRIVATE flag

Ackerley Tng wrote:
> Test that GUEST_MEMFD_FLAG_INIT_PRIVATE is only valid when
> GUEST_MEMFD_FLAG_SUPPORT_SHARED is set.
> 
> Change-Id: I506e236a232047cfaee17bcaed02ee14c8d25bbb
> Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
> ---
>  .../testing/selftests/kvm/guest_memfd_test.c  | 36 ++++++++++++-------
>  1 file changed, 24 insertions(+), 12 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index 60aaba5808a5..bf2876cbd711 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -401,13 +401,31 @@ static void test_with_type(unsigned long vm_type, uint64_t guest_memfd_flags,
>  	kvm_vm_release(vm);
>  }
>  
> +static void test_vm_with_gmem_flag(struct kvm_vm *vm, uint64_t flag,
> +				   bool expect_valid)
> +{
> +	size_t page_size = getpagesize();
> +	int fd;
> +
> +	fd = __vm_create_guest_memfd(vm, page_size, flag);
> +
> +	if (expect_valid) {
> +		TEST_ASSERT(fd > 0,
> +			    "guest_memfd() with flag '0x%lx' should be valid",
> +			    flag);
> +		close(fd);
> +	} else {
> +		TEST_ASSERT(fd == -1 && errno == EINVAL,
> +			    "guest_memfd() with flag '0x%lx' should fail with EINVAL",
> +			    flag);
> +	}
> +}
> +
>  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 (!(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(vm_type)))
>  		return;
> @@ -415,17 +433,11 @@ static void test_vm_type_gmem_flag_validity(unsigned long vm_type,
>  	vm = vm_create_barebones_type(vm_type);
>  
>  	for (flag = BIT(0); flag; flag <<= 1) {
> -		fd = __vm_create_guest_memfd(vm, page_size, flag);
> +		test_vm_with_gmem_flag(vm, flag, flag & expected_valid_flags);
>  
> -		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 == -1 && errno == EINVAL,
> -				    "guest_memfd() with flag '0x%lx' should fail with EINVAL",
> -				    flag);
> +		if (flag == GUEST_MEMFD_FLAG_SUPPORT_SHARED) {
> +			test_vm_with_gmem_flag(
> +				vm, flag | GUEST_MEMFD_FLAG_INIT_PRIVATE, true);

I don't understand the point of this check.  In 2/51 we set 
GUEST_MEMFD_FLAG_INIT_PRIVATE when GUEST_MEMFD_FLAG_SUPPORT_SHARED is set.

When can this check ever fail?

Ira