[PATCH v2] powerpc: Don't clobber fr0/vs0 during fp|altivec register save

[Michael Ellerman]

Christophe Leroy <christophe.leroy at csgroup.eu> writes:
> Le 27/11/2023 à 19:39, Timothy Pearson a écrit :
>> Just wanted to check back and see if this patch was going to be
>> queued up soon?  We're still having to work around / advertise the
>> data destruction issues the underlying bug is causing on e.g. Debian
>> Stable.
>
> Has any agreement been reach on the final solution ? Seeing the many 
> discussion on patch v2 I had the feeling that it was not the final solution.

The actual patch is fine I think.

The discussion was about improving the explanation of exactly what's
happening in the change log, and whether there is a larger bug causing
FP corruption unrelated to io-uring.

I'm now reasonably confident there's no detectable corruption of fr0
happening except via the io-uring -> clone path.

It's still a bad bug for us to corrupt fr0 across sys_clone(), but in
practice it doesn't affect userspace because fr0 is volatile across
function calls.

cheers