Re: [PATCH] KVM: SEV: drop FOLL_LONGTERM for encrypted region registration

[David Hildenbrand (Arm)]

On 7/10/26 15:05, Lorenzo Stoakes wrote:
> On Fri, Jul 10, 2026 at 02:57:55PM +0200, David Hildenbrand (Arm) wrote:
>> On 7/9/26 17:44, Lorenzo Stoakes wrote:
>>>
>>> OK as long as that's made clear in the patch, commit message, comments etc. :)
>>>
>>>
>>> Ack yeah I assumed it was a quick proof of concept and just overlooked it :P
>>>
>>>
>>> Thanks!
>>>
>>>
>>> hmm but we have FOLL_LONGTERM as an adjunct to FOLL_PIN (doesn't make sense
>>> without - any checks that exist for that btw should be extended to this noew
>>> flag).
>>>
>>> Also don't we want to encode the legacy aspect here?
>>>
>>> Maybe FOLL_LONGTERM_LEGACY_READONLY? Naming is hard :)
>>
>> I'm confused about the _READONLY, well. and the FOLL_PIN_NO_GUP_WRITE.
>>
>> We want to longterm write-pin.
>>
>> @Pankaj, how come you would call this "FOLL_PIN_NO_GUP_WRITE" -- why "no GUP
>> write" ?
>>
>> I agree that someting like FOLL_LONGTERM_LEGACY_* is the right thing to do, but
>> I don't see where this is "no write" or "readonly" ?
> 
> I based it on Gupta saying 'without kernel GUP writes, and therefore not
> impacting dirty tracking'
> 
> I mean I think we definitely need some clarification here yes :)
> 
> Not really got the bandwidth to dig deep into GUP again :P

I think the KVM gueest *will* write to these pages.

By disallowing writable LONGTERM pins on FSes we broke one existing use case
that was relying on that to work.

-- 
Cheers,

David