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

On Tue Nov 28, 2023 at 10:59 AM AEST, Michael Ellerman wrote:

Christophe Leroy [off-list ref] writes:

quoted

Le 27/11/2023 à 19:39, Timothy Pearson a écrit :

quoted

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.

One thing I said is maybe we should remove the "register save" concept
entirely and always giveup. But that would not be suitable for a minimal
fix. I didn't mean it as an alternate fix.

Even if we did always giveup in future, this patch still gives a nicer
API. There would have to be a noticable performance advantage to not
restoring fr0/vs0 after saving before we'd think about changing it back
to clobber, since that encourages foot shooting.

Thanks,
Nick