[PATCH RFC v4 35/44] KVM: selftests: Test that not specifying a conversion flag scrambles memory contents

Ackerley Tng
2026-03-26T22:25:37Z

When using KVM_SET_MEMORY_ATTRIBUTES2, not specifying flags for the ioctl
implies no guarantees on memory contents.

For KVM_X86_SW_PROTECTED_VM, this mode is implemented by scrambling
contents of converted memory ranges. Add a test to check that the
unspecified conversion mode was handled in KVM by checking the expected
behavior, that existing memory contents are scrambled.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
.../selftests/kvm/guest_memfd_conversions_test.c | 28 ++++++++++++++++++++++
1 file changed, 28 insertions(+)

diff --git a/tools/testing/selftests/kvm/guest_memfd_conversions_test.c b/tools/testing/selftests/kvm/guest_memfd_conversions_test.c
index 277b122ec294c..4b2f00afda01c 100644
--- a/tools/testing/selftests/kvm/guest_memfd_conversions_test.c
+++ b/tools/testing/selftests/kvm/guest_memfd_conversions_test.c
@@ -512,6 +512,34 @@ GMEM_CONVERSION_TEST_INIT_SHARED(convert_to_private_does_not_support_zero)
TEST_ASSERT_EQ(error_offset, start_offset);
}

+GMEM_CONVERSION_TEST_INIT_SHARED(convert_mode_unspecified_scrambles)
+{
+ loff_t error_offset = -1ul;
+ int ret;
+
+ test_shared(t, 0, 0, 'A', 'B');
+ ret = __gmem_set_private(t->gmem_fd, 0, nr_pages * page_size,
+ &error_offset, 0);
+ TEST_ASSERT_EQ(ret, 0);
+ TEST_ASSERT_EQ(error_offset, -1ul);
+
+ /*
+ * Since the content mode 0 scrambles data in memory, there is
+ * a small chance that this test will falsely fail when the
+ * scrambled value matches the initial value.
+ */
+ run_guest_do_rmw(t->vcpu, 0, 'B', 'C', true);
+
+ ret = __gmem_set_shared(t->gmem_fd, 0, nr_pages * page_size,
+ &error_offset, 0);
+ TEST_ASSERT_EQ(ret, 0);
+ TEST_ASSERT_EQ(error_offset, -1ul);
+
+ /* Same small chance of falsely failing test applies here. */
+ TEST_ASSERT(READ_ONCE(t->mem[0]) != 'C',
+ "Conversion without specifying mode should scramble memory.");
+}
+
int main(int argc, char *argv[])
{
TEST_REQUIRE(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(KVM_X86_SW_PROTECTED_VM));

--
2.53.0.1018.g2bb0e51243-goog