Re: [PATCH 0/2] x86/fpu: Allow restoring signal frames with larger xstate_size

[Andrei Vagin]

On Tue, Sep 29, 2026 at 4:57 PM Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Tue, Sep 29, 2026 at 11:26:19PM +0000, Andrei Vagin wrote:
> > When a process is checkpointed on one machine and restored on another
> > (e.g., via CRIU during container/process migration), any signal frame on
> > its stack carries the xstate layout of the source CPU.
> >
> > Commit fd14edd82077 ("x86/fpu: Pre-fault only required size of xstate
> > buffer") enabled restoring signal frames created on CPUs with a smaller
> > xstate_size than the destination host's default. However,
> > check_xstate_in_sigframe() still enforces that a signal frame's
> > xstate_size must not exceed the current task's fpstate->user_size.
>
> Hmm, what happened? Change of heart after the fact?
>
> So I guess I am zapping fd14edd82077 from tip:x86/fpu now and then we test
> some more before we try this again?

I think it is a misunderstanding. This series is actually the next step.
The first series enabled migrating workloads from older CPUs to newer
ones. This series enables migrating workloads from newer CPUs to older
ones.

Thanks,
Andrei