linux-kernel - [PATCH 0/1] x86/fpu: Allow clearcpuid= to clear several bits

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Date:   Wed, 22 Apr 2020 13:03:18 +0100
From:   John Haxby <john.haxby@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>
Cc:     x86@...nel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, John Haxby <john.haxby@...cle.com>
Subject: [PATCH 0/1] x86/fpu: Allow clearcpuid= to clear several bits

Back in the mists of time, well, prior to 4.14.9, you could put clearcpuid=N
several times on the command line to clear several CPUID bits.  Unfortunately,
there was a problem with the way that this was done which meant XSAVE, in
particular, wasn't cleared early enough.  This was fixed in 0c2a3913d6f5
("x86/fpu: Parse clearcpuid= as early XSAVE argument").  Unfortunately that
also meant that only one bit could be cleared.

This patch mostly fixes that.  Gone is the old, anachronistic, multiple
clearcpuid= arguments to be replaced by a single clearcpuid=BITNUM[,BITNUM,...]
argument.  It's no longer possible to clear perhaps dozens of flags with a very
long kernel command line, but you can clear up to about eight bits now instead
of just one.

jch

John Haxby (1):
  x86/fpu: Allow clearcpuid= to clear several bits

 .../admin-guide/kernel-parameters.txt         | 24 ++++++++++---------
 arch/x86/kernel/fpu/init.c                    | 18 ++++++++------
 2 files changed, 24 insertions(+), 18 deletions(-)

-- 
2.25.3