Re: [PATCH v8 46/46] KVM: selftests: Update private memory exits test to work with per-gmem attributes

[Fuad Tabba]

On Fri, 19 Jun 2026 at 01:32, Ackerley Tng via B4 Relay
<devnull+ackerleytng.google.com@xxxxxxxxxx> wrote:
>
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
>
> Skip setting memory to private in the private memory exits test when using
> per-gmem memory attributes, as memory is initialized to private by default
> for guest_memfd, and using vm_mem_set_private() on a guest_memfd instance
> requires creating guest_memfd with GUEST_MEMFD_FLAG_MMAP (which is totally
> doable, but would need to be conditional and is ultimately unnecessary).
>
> Expect an emulated MMIO instead of a memory fault exit when attributes are
> per-gmem, as deleting the memslot effectively drops the private status,
> i.e. the GPA becomes shared and thus supports emulated MMIO.
>
> Skip the "memslot not private" test entirely, as private vs. shared state
> for x86 software-protected VMs comes from the memory attributes themselves,
> and so when doing in-place conversions there can never be a disconnect
> between the expected and actual states.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>

Cheers,
/fuad

> ---
>  .../selftests/kvm/x86/private_mem_kvm_exits_test.c | 36 ++++++++++++++++++----
>  1 file changed, 30 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/x86/private_mem_kvm_exits_test.c b/tools/testing/selftests/kvm/x86/private_mem_kvm_exits_test.c
> index 10db9fe6d9063..70ed16066c63e 100644
> --- a/tools/testing/selftests/kvm/x86/private_mem_kvm_exits_test.c
> +++ b/tools/testing/selftests/kvm/x86/private_mem_kvm_exits_test.c
> @@ -62,8 +62,9 @@ static void test_private_access_memslot_deleted(void)
>
>         virt_map(vm, EXITS_TEST_GVA, EXITS_TEST_GPA, EXITS_TEST_NPAGES);
>
> -       /* Request to access page privately */
> -       vm_mem_set_private(vm, EXITS_TEST_GPA, EXITS_TEST_SIZE);
> +       /* Request to access page privately. */
> +       if (!kvm_has_gmem_attributes)
> +               vm_mem_set_private(vm, EXITS_TEST_GPA, EXITS_TEST_SIZE);
>
>         pthread_create(&vm_thread, NULL,
>                        (void *(*)(void *))run_vcpu_get_exit_reason,
> @@ -74,10 +75,26 @@ static void test_private_access_memslot_deleted(void)
>         pthread_join(vm_thread, &thread_return);
>         exit_reason = (u32)(u64)thread_return;
>
> -       TEST_ASSERT_EQ(exit_reason, KVM_EXIT_MEMORY_FAULT);
> -       TEST_ASSERT_EQ(vcpu->run->memory_fault.flags, KVM_MEMORY_EXIT_FLAG_PRIVATE);
> -       TEST_ASSERT_EQ(vcpu->run->memory_fault.gpa, EXITS_TEST_GPA);
> -       TEST_ASSERT_EQ(vcpu->run->memory_fault.size, EXITS_TEST_SIZE);
> +       /*
> +        * If attributes are tracked per-gmem, deleting the memslot that points
> +        * at the gmem instance effectively makes the memory shared, and so the
> +        * read should trigger emulated MMIO.
> +        *
> +        * If attributes are tracked per-VM, deleting the memslot shouldn't
> +        * affect the private attribute, and so KVM should generate a memory
> +        * fault exit (emulated MMIO on private GPAs is disallowed).
> +        */
> +       if (kvm_has_gmem_attributes) {
> +               TEST_ASSERT_EQ(exit_reason, KVM_EXIT_MMIO);
> +               TEST_ASSERT_EQ(vcpu->run->mmio.phys_addr, EXITS_TEST_GPA);
> +               TEST_ASSERT_EQ(vcpu->run->mmio.len, sizeof(u64));
> +               TEST_ASSERT_EQ(vcpu->run->mmio.is_write, false);
> +       } else {
> +               TEST_ASSERT_EQ(exit_reason, KVM_EXIT_MEMORY_FAULT);
> +               TEST_ASSERT_EQ(vcpu->run->memory_fault.flags, KVM_MEMORY_EXIT_FLAG_PRIVATE);
> +               TEST_ASSERT_EQ(vcpu->run->memory_fault.gpa, EXITS_TEST_GPA);
> +               TEST_ASSERT_EQ(vcpu->run->memory_fault.size, EXITS_TEST_SIZE);
> +       }
>
>         kvm_vm_free(vm);
>  }
> @@ -88,6 +105,13 @@ static void test_private_access_memslot_not_private(void)
>         struct kvm_vcpu *vcpu;
>         u32 exit_reason;
>
> +       /*
> +        * Accessing non-private memory as private with a software-protected VM
> +        * isn't possible when doing in-place conversions.
> +        */
> +       if (kvm_has_gmem_attributes)
> +               return;
> +
>         vm = vm_create_shape_with_one_vcpu(protected_vm_shape, &vcpu,
>                                            guest_repeatedly_read);
>
>
> --
> 2.55.0.rc0.738.g0c8ab3ebcc-goog
>
>