Re: [PATCH v15 13/23] KVM: selftests: Support guest_memfd in-place conversion

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 10/10/2026 11:32 AM, Binbin Wu wrote:
> On 10/2/2026 3:37 AM, Lisa Wang wrote:
>> With guest_memfd in-place conversion, the memory region can be set as
>> shared, eliminating the need for dual-backed memory.
>>
>> By setting the region to shared initially, the KVM selftest framework
>> can populate the mmap()-ed guest_memfd memory just like any standard
>> memory provider.
>>
>> For CoCo VMs, pages that need to be private are explicitly set to
>> private before executing the VM.
>>
>> Signed-off-by: Lisa Wang <wyihan@google.com>
>> ---
>>  tools/testing/selftests/kvm/lib/kvm_util.c         | 20 ++++++++++++++------
>>  tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c |  6 +++++-
>>  2 files changed, 19 insertions(+), 7 deletions(-)
>>
>> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
>> index 7625908caf21..f474664b5d92 100644
>> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
>> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
>> @@ -494,8 +494,10 @@ struct kvm_vm *__vm_create(struct vm_shape shape, u32 nr_runnable_vcpus,
>>  	u64 nr_pages = vm_nr_pages_required(shape.mode, nr_runnable_vcpus,
>>  						 nr_extra_pages);
>>  	struct userspace_mem_region *slot0;
>> +	u64 gmem_flags = 0;
>>  	struct kvm_vm *vm;
>> -	int i, flags;
>> +	int flags = 0;
>> +	int i;
>>  
>>  	kvm_set_files_rlimit(nr_runnable_vcpus);
>>  
>> @@ -505,14 +507,20 @@ struct kvm_vm *__vm_create(struct vm_shape shape, u32 nr_runnable_vcpus,
>>  	vm = ____vm_create(shape);
>>  
>>  	/*
>> -	 * Force GUEST_MEMFD for the primary memory region if necessary, e.g.
>> -	 * for CoCo VMs that require GUEST_MEMFD backed private memory.
>> +	 * Force GUEST_MEMFD for the primary memory region if necessary, and
>> +	 * initialize it as shared if in-place conversion is supported, so the
>> +	 * selftest framework can populate it exactly like other memory
>> +	 * providers.
>>  	 */
>> -	flags = 0;
>> -	if (is_guest_memfd_required(shape))
>> +	if (is_guest_memfd_required(shape)) {
>>  		flags |= KVM_MEM_GUEST_MEMFD;
>> +		if (kvm_has_gmem_attributes)
>> +			gmem_flags |= GUEST_MEMFD_FLAG_INIT_SHARED |
>> +				      GUEST_MEMFD_FLAG_MMAP;
>> +	}
>>  
>> -	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, 0, 0, nr_pages, flags);
>> +	vm_mem_add(vm, VM_MEM_SRC_ANONYMOUS, 0, 0, nr_pages, flags,
>> +		   -1, 0, gmem_flags);
> This is common for both TDX and SNP, does it break SNP?

As I commented in the v14[1], I still believe this part belongs to gmem in-place
conversion series. Without this part, I think the SNP selftests will fail if
in-place conversion is enabled.

Ackerley, did you test SNP selftests?


[1] https://lore.kernel.org/kvm/f7b3a63c-7a1d-445f-b062-4cea5343d266@intel.com/