Re: [PATCH v2] vdso: Remove struct getcpu_cache

[Andy Lutomirski]

On Mon, Oct 13, 2025 at 12:45 PM H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>
> On 2025-10-13 10:14, Andy Lutomirski wrote:
> >
> > I don't actually remember whether the kernel ever used this.  It's
> > possible that there are ancient kernels where passing a wild, non-null
> > pointer would blow up.  But it's certainly safe to pass null, and it's
> > certainly safe for the kernel to ignore the parameter.
> >
>
> One could imagine an architecture which would have to execute an actual system
> call wanting to use this, but on x86 it is pointless -- even the LSL trick is
> much faster than a system call, and once you account for whatever hassle you
> would have to deal with do make the cache make sense (probably having a global
> generation number and/or a timestamp to expire it) it well and truly makes no
> sense.

The global timestamp would just be some field in the vvar area, which
we have plenty of anyway.

But I agree, accelerating getcpu is pointless.  In any case, anything
that historically thought it really really wanted accelerated getcpu
can, and probably does, use rseq these days.

--Andy