[PATCH RFC v4 44/44] KVM: selftests: Update private memory exits test to work with per-gmem attributes

Ackerley Tng
2026-03-26T22:25:55Z

From: Sean Christopherson <seanjc@google.com>

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@google.com>
---
.../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 cbcb5d6d04436..ed1bf27d149dc 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, 0);
+ /* Request to access page privately. */
+ if (!kvm_has_gmem_attributes)
+ vm_mem_set_private(vm, EXITS_TEST_GPA, EXITS_TEST_SIZE, 0);

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 = (uint32_t)(uint64_t)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(uint64_t));
+ 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;
uint32_t 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);

--
2.53.0.1018.g2bb0e51243-goog