Re: [PATCH v10 40/41] KVM: selftests: Update private_mem_conversions_test to mmap() guest_memfd

Xiaoyao Li [off-list ref] writes:

On 8/25/2026 5:32 PM, Ackerley Tng wrote:

quoted

Sean Christopherson [off-list ref] writes:

quoted

On Fri, Aug 21, 2026, Xiaoyao Li wrote:

quoted

On 8/8/2026 5:53 AM, Ackerley Tng via B4 Relay wrote:

quoted

From: Ackerley Tng<redacted>

Update the private memory conversions selftest to also test conversions
that are done "in-place" via per-guest_memfd memory attributes. In-place
conversions require the host to be able to mmap() the guest_memfd so that
the host and guest can share the same backing physical memory.

This includes several updates, that are conditioned on the system
supporting per-guest_memfd attributes (kvm_has_gmem_attributes):

1. Set up guest_memfd requesting MMAP and INIT_SHARED.

If I understand correctly, even with in-place gmem, the model that shared
memory comes from the userspace_addr and private memory comes from gmem can
still work without passing GUEST_MEMFD_FLAG_MMAP flag.

Since this model is not prohibited by KVM. I think we should keep the
testcase for this model to ensure test coverage?

+1.  Deprecated doesn't mean unsupported.

The original test case was for non-in-place conversion, which wasn't
removed, it still passes.

It only passes when

   /sys/module/kvm/parameters/gmem_in_place_conversion=n

It fails as below when gmem_in_place_conversion=y

./tools/testing/selftests/kvm/x86/private_mem_conversions_test
Random seed: 0x7eace343

==== Test Assertion Failure ====
   x86/private_mem_conversions_test.c:46: mem[i] == pattern
   pid=288745 tid=288747 errno=4 - Interrupted system call
      1	0x000000000040426a: memcmp_h at private_mem_conversions_test.c:46
      2	 (inlined by) __test_mem_conversions at
private_mem_conversions_test.c:356
      3	0x00007f2ea2c89c01: ?? ??:0
      4	0x00007f2ea2d0ec3f: ?? ??:0
   Host expected 0xaa at gpa 0x100000000, got 0x0

quoted

Is the ask to also test, under kvm_has_gmem_attributes aka
gmem_in_place_conversion, to have guest_memfd used as purely for private
memory and have shared memory taken from somewhere else completely?

I can rephrase the changelog and change the code to clarify that this
patch is meant to specifically test in-place conversion with MMAP, the
intended usage of in-place conversions.

The ask to test gmem for private and something else for shared seems
like a different test that can be added separately, perhaps in a
follow-up series?

I see it as the fix for existing testcase, not another new test. And the
fix is simple:
1. change to use vm_mem_set_memory_attributes() to set memory attribute.
2. pass GUEST_MEMFD_FLAG_INIT_SHARED to create the gmem because this
test expects the initial state of the gfn is shared.

I understand now. I worked it out, I should be able to post v11
tomorrow, just need a little bit more testing.