[RFC PATCH v1 0/8] liveupdate: kvm: Guest_memfd preservation

[Ackerley Tng]

Sean Christopherson <seanjc at google.com> writes:

>>
>> [...snip...]
>>
>> we have one open Question left:
>> 1. How to check guest_memfd is fully shared.
>>
>> [...snip...]
>>
>
> Given that lack of support isn't going to be limited to _just_ guest_memfd,
> simply disallow preservation if the VM supports private memory:
>
> 	if (kvm_arch_has_private_mem(kvm))
> 		return -EOPNOTSUPP;

Makes sense. Tarun this was the other option that I was suggesting when
we discussed offline.

I think (?) it is possible to create a fully-private guest_memfd for a
non-Confidential VM, and even after conversion lands, for both
vm_memory_attributes=true and vm_memory_attributes=false.

In that case, your preservation series can still preserve memory tracked
as private by guest_memfd but not used as private, right?

I don't think anyone will use this combination before guest_memfd
write() support lands, we just need to make sure there's no kernel crash
or corruption in this case.