linux-kernel - Re: [PATCH] [PATCH] x86: Don't clobber top of pt

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Date:	Thu, 01 Nov 2012 16:37:21 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jan Beulich <jbeulich@...e.com>
Cc:	sqazi@...gle.com, peterz@...radead.org, tglx@...utronix.de,
	torvalds@...ux-foundation.org, hpa@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [PATCH] x86: Don't clobber top of pt_regs in nested NMI

On Thu, 2012-11-01 at 19:53 +0000, Jan Beulich wrote:
> >>> Steven Rostedt <rostedt@...dmis.org> 11/01/12 2:04 AM >>>
> >On Mon, 2012-10-01 at 17:29 -0700, Salman Qazi wrote:
> >> @@ -1826,12 +1832,15 @@ repeat_nmi:
> >>       * is benign for the non-repeat case, where 1 was pushed just above
> >>       * to this very stack slot).
> >>       */
> >> -    movq $1, 5*8(%rsp)
> >> +    movq $1, 10*8(%rsp)
> >>  
> >>      /* Make another copy, this one may be modified by nested NMIs */
> >> +    addq $(10*8), %rsp
> >
> >This breaks the CFI magic.
> >
> >>      .rept 5
> >> -    pushq_cfi 4*8(%rsp)
> >> +    pushq_cfi -6*8(%rsp)
> >>      .endr
> >> +    subq $(5*8), %rsp
> >
> >So does this.
> >
> >This needs to be annotated correctly before I can push it out. But the
> >good news is, I stressed tested this change, and it all works out.
> >
> >Jan, can you help out here?
> 
> There doesn't appear to be anything special about these adjustments, so I
> don't see what help would be required here - it ought to be the normal use
> of CFI_ADJUST_CFA_OFFSET that needs adding.

Even the simple CFI adjustments look like magic to me :-)  OK, I'll
update the patch and send it out. I'll Cc you in case I screw up even
the most simple case ;-)

-- Steve


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