Re: [PATCH v10 01/28] x86/fpu/xstate: Fix the state copy function to the XSTATE buffer
From: Thomas Gleixner
Date: Fri Oct 01 2021 - 08:44:49 EST
Chang,
On Wed, Aug 25 2021 at 08:53, Chang S. Bae wrote:
> Harden copy_uabi_to_xstate() so that it can handle the case where
> __raw_xsave() returns NULL.
That's an implementation detail, but does not explain why this can
happen and what this patch is about.
> This does not happen in practice today, but theoretically could happen
> in the future.
So what does the patch "fix"? When the subject says "Fix..." then I'm
expecting a bug in the code to be fixed.
There is none because the use case which can trip over this does not
exist today. You are adding it later.
Subject: .....: Prepare copy_uabi_to_xstate() to handle dynamic features
or something like that along with a reasonable explanation.
But in a later patch you add in the very same function:
> + hdr.xfeatures &= fpu->state_mask;
which prevents that already because __raw_xsave_addr() is not invoked
for the zeroed bits in hdr.xfeatures:
> if (hdr.xfeatures & mask) {
> void *dst = __raw_xsave_addr(xsave, i);
Confused.
I'm not against the change per se, but I'm not accepting changelogs
which make no sense at all. News at 11.
Thanks,
tglx