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

[Binbin Wu]

On 5/17/2025 1:42 AM, Ackerley Tng wrote:
> Ira Weiny <ira.weiny@xxxxxxxxx> 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@xxxxxxxxxx>
> > > ---
> > >   .../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.
Maybe it's more clear to move this case out of the loop?


> 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.