Re: [RFC PATCH v1 07/37] KVM: Introduce KVM_SET_MEMORY_ATTRIBUTES2

[Ackerley Tng]

Sean Christopherson <seanjc@xxxxxxxxxx> writes:

> On Fri, Oct 24, 2025, Ackerley Tng wrote:
>> Sean Christopherson <seanjc@xxxxxxxxxx> writes:
>> > @@ -486,6 +488,7 @@ struct kvm_vm *__vm_create(struct vm_shape shape, uint32_t nr_runnable_vcpus,
>> >         }
>> >         guest_rng = new_guest_random_state(guest_random_seed);
>> >         sync_global_to_guest(vm, guest_rng);
>> > +       sync_global_to_guest(vm, kvm_has_gmem_attributes);
>> 
>> I ported this [1] except for syncing this value to the guest, because I
>> think the guest shouldn't need to know this information,
>
> KVM selftests are about practically and testing, what information should or
> shouldn't be available to a test from e.g. a safety perspective is completely
> irrelevant.  In fact, one of the biggest advantages of selftests over KUT is
> that the guest side can know _exactly_ what's going on in the host.
>
> See the usage in 1850e3da4b03 ("KVM: selftests: Update private_mem_conversions_test
> to mmap() guest_memfd") from:
>
>   https://github.com/sean-jc/linux.git x86/gmem_inplace
>
>> the host should decide what to do. I think, if the guests really need to know
>> this, the test itself can do the syncing.
>
> Why force tests to do extra work, and potentially introduce subtle bugs due to
> state being stale?

Adding it back. Thanks!

This variable should be sync-able for TDX selftests as well since the
value should be synced before the TD image is loaded.