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

[Sean Christopherson <seanjc@google.com>]

On Wed, Jul 01, 2026, Xiaoyao Li wrote:
> On 7/1/2026 2:18 AM, Ackerley Tng wrote:
> > > > 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.
> 
> But before gmem in-place conversion, i.e., per-gmem attribute,
> GUEST_MEMFD_FLAG_INIT_SHARED is not supported/valid for Coco VMs.
> > > 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?

No.  Unless supporting out-of-place conversion requires orders of magnitude more
effort than just supporting in-place conversion, selftests should play nice with
both.

> Well, then all the TDX and SNP selftest will be skipped on the kernel with
> gmem_in_place_conversion=false.

Exactly.  They'll also be unusable on previous kernels.

Deprecating per-VM PRIVATE tracking does not mean dropping support.  We won't be
able to drop support for years, if ever.  And so from a testing perspective, we
absolutely need to validate both models (again, within reason).