Re: [PATCH v7 20/42] KVM: SEV: Make 'uaddr' parameter optional for KVM_SEV_SNP_LAUNCH_UPDATE

[Ackerley Tng]

Suzuki K Poulose <suzuki.poulose@xxxxxxx> writes:

>
> [...snip...]
>
>> +In the case where ``type`` is KVM_SEV_SNP_PAGE_TYPE_ZERO, ``uaddr`` will be
>> +ignored completely. Otherwise, ``uaddr`` is required if
>> +kvm.vm_memory_attributes=1 and optional if kvm.vm_memory_attributes=0, since
>> +in the latter case guest memory can be initialized directly from userspace
>> +prior to converting it to private and passing the GPA range on to this
>> +interface.
>
> Just to confirm, so the sev_gmem_prepare doesn't destroy the contents in
> the process of making it "private" ? i.e., the contents of a SNP shared
> page are preserved while transitioning to "SNP Private" (via RMP
> update).
>
> Suzuki
>

The following is the guest_memfd perspective, I didn't look at the SNP
spec:

Do you mean specifically for KVM_SEV_SNP_PAGE_TYPE_ZERO, or for any
type?

guest_memfd has no plans to do any special zeroing based on type.

guest_memfd decoupled zeroing from preparation a while ago (Michael had
some patches), so zeroing is supposed to be once during folio ownership
by guest_memfd, tracked by the uptodate flag, and preparation is tracked
outside of guest_memfd. So far only SNP does preparation.

>
>
>>
>> [...snip...]
>>