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Message-ID: <682792986c060_34533a294d1@iweiny-mobl.notmuch>
Date: Fri, 16 May 2025 14:31:36 -0500
From: Ira Weiny <ira.weiny@...el.com>
To: Ackerley Tng <ackerleytng@...gle.com>, Ira Weiny <ira.weiny@...el.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:
> Ira Weiny <ira.weiny@...el.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@...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
>
> 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.
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