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

[Ackerley Tng]

Xiaoyao Li <xiaoyao.li@xxxxxxxxx> writes:

> On 6/16/2026 7:46 AM, Ackerley Tng wrote:
>> Lisa Wang <wyihan@xxxxxxxxxx> 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.
>

GUEST_MEMFD_FLAG_INIT_SHARED was introduced before guest_memfd in-place
conversions, so I think it's orthogonal to whether memory attributes is
per-gmem.

> we need to check KVM_CAP_GUEST_MEMFD_FLAGS or kvm_has_gmem_attributes.

I think we do want to deprecate the non-in-place-conversions setup, so
how about inserting a TEST_REQIRE(kvm_has_gmem_attributes) here?