Re: [RFC PATCH v2 03/51] KVM: selftests: Update guest_memfd_test for INIT_PRIVATE flag

[Ackerley Tng <ackerleytng@google.com>]

Ira Weiny <ira.weiny@intel.com> writes:

> 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@google.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

In 02/51, GUEST_MEMFD_FLAG_INIT_PRIVATE is not set by default,
GUEST_MEMFD_FLAG_INIT_PRIVATE is set as one of the valid_flags.

The intention is that GUEST_MEMFD_FLAG_INIT_PRIVATE is only valid if
GUEST_MEMFD_FLAG_SUPPORT_SHARED is requested by userspace.

In this test, the earlier part before the if block calls
test_vm_with_gmem_flag() all valid flags, and that already tests
GUEST_MEMFD_FLAG_SUPPORT_SHARED individually.

Specifically if GUEST_MEMFD_FLAG_SUPPORT_SHARED is set, this if block
adds a test for when both GUEST_MEMFD_FLAG_SUPPORT_SHARED and
GUEST_MEMFD_FLAG_INIT_PRIVATE are set, and sets that expect_valid is
true.

This second test doesn't fail, it is meant to check that the kernel
allows the pair of flags to be set. Hope that makes sense.