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

On 8/25/2026 5:32 PM, Ackerley Tng wrote:
> Sean Christopherson <[email protected]> writes:
> 
>> On Fri, Aug 21, 2026, Xiaoyao Li wrote:
>>> On 8/8/2026 5:53 AM, Ackerley Tng via B4 Relay wrote:
>>>> From: Ackerley Tng<[email protected]>
>>>>
>>>> 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

> 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.

---8<----
diff --git 
a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c 
b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
index cf50e9a332c5..fbd6c63d21cf 100644
--- a/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
+++ b/tools/testing/selftests/kvm/x86/private_mem_conversions_test.c
@@ -307,7 +307,7 @@ static void handle_exit_hypercall(struct kvm_vcpu *vcpu)
                 vm_guest_mem_fallocate(vm, gpa, size, map_shared);

         if (set_attributes)
-               vm_set_memory_attributes(vm, gpa, size,
+               vm_mem_set_memory_attributes(vm, gpa, size,
                                          map_shared ? 0 : 
KVM_MEMORY_ATTRIBUTE_PRIVATE);
         run->hypercall.ret = 0;
  }
@@ -382,6 +382,7 @@ static void test_mem_conversions(enum 
vm_mem_backing_src_type src_type, u32 nr_v
         const size_t slot_size = memfd_size / nr_memslots;
         struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
         pthread_t threads[KVM_MAX_VCPUS];
+       u64 gmem_flags = 0;
         struct kvm_vm *vm;
         int memfd, i;

@@ -397,7 +398,10 @@ static void test_mem_conversions(enum 
vm_mem_backing_src_type src_type, u32 nr_v

         vm_enable_cap(vm, KVM_CAP_EXIT_HYPERCALL, (1 << 
KVM_HC_MAP_GPA_RANGE));

-       memfd = vm_create_guest_memfd(vm, memfd_size, 0);
+       if (kvm_has_gmem_attributes)
+               gmem_flags = GUEST_MEMFD_FLAG_INIT_SHARED;
+
+       memfd = vm_create_guest_memfd(vm, memfd_size, gmem_flags);

         for (i = 0; i < nr_memslots; i++)
                 vm_mem_add(vm, src_type, BASE_DATA_GPA + slot_size * i,