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

[Ira Weiny <ira.weiny@intel.com>]

Ackerley Tng wrote:
> 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.

Ah My mistake I read that too quickly.

Thanks,
Ira

> 
> 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.