linux-kernel - Re: [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling with IRQ state tracing enabled

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Date:   Wed, 29 Nov 2017 19:08:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling
 with IRQ state tracing enabled

On Wed, Nov 29, 2017 at 09:57:43AM -0800, Andy Lutomirski wrote:
> On Tue, Nov 28, 2017 at 11:09 PM, Ingo Molnar <mingo@...nel.org> wrote:

> > On a related note, we should definitely extend the 'intended GS state' annotation
> > comments I did in this patch to all SWAPGS instances - this way code review has a
> > much higher chance of finding discrepancies between intent and actual code.
> 
> Agreed.  I'll send a patch.

Alternatively we could do something like:

  SWITCH_TO_KERNEL_GS
  SWITCH_TO_USER_GS

and have them do the SWAPGS with an (optional) assertion of the actual
GS.