Re: [PATCH v13 13/22] KVM: selftests: Set first memory region as shared if guest_memfd

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

On 6/16/2026 7:46 AM, Ackerley Tng wrote:
> Lisa Wang <wyihan@google.com> writes:
> 
>> Set the initial state of the first memory region as shared if it is
>> backed by guest_memfd, so that the KVM selftest framework functions can
>> populate mmap()-ed guest_memfd memory the same way memory from other
>> memory providers are populated.
>>
>> For CoCo VMs, pages that need to be private are explicitly set to
>> private before executing the VM.
>>
>>
>> [...snip...]
>>
>> @@ -495,14 +497,16 @@ 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 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;
>> +		gmem_flags |= GUEST_MEMFD_FLAG_INIT_SHARED;
>> +	}
>>
> 
> Just noticed this while hacking some SNP tests.
> 
>> -	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);
>>   	for (i = 0; i < NR_MEM_REGIONS; i++)
>>   		vm->memslots[i] = 0;
>>
>>
>> --
>> 2.54.0.746.g67dd491aae-goog
> 
> I think this patch should fully buy into in-place conversions, so we
> need to also set GUEST_MEMFD_FLAG_MMAP:
> 
> @@ -483,6 +483,7 @@ 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);
> +	enum vm_mem_backing_src_type src_type = VM_MEM_SRC_ANONYMOUS;
>   	struct userspace_mem_region *slot0;
>   	u64 gmem_flags = 0;
>   	struct kvm_vm *vm;
> @@ -503,10 +504,16 @@ struct kvm_vm *__vm_create(struct vm_shape
> shape, u32 nr_runnable_vcpus,
>   	 */
>   	if (is_guest_memfd_required(shape)) {
>   		flags |= KVM_MEM_GUEST_MEMFD;
> -		gmem_flags |= GUEST_MEMFD_FLAG_INIT_SHARED;
> +		gmem_flags |= GUEST_MEMFD_FLAG_INIT_SHARED | GUEST_MEMFD_FLAG_MMAP;

GUEST_MEMFD_FLAG_INIT_SHARED is valid only when the memory attributes is 
per-gmem.

we need to check KVM_CAP_GUEST_MEMFD_FLAGS or kvm_has_gmem_attributes.