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

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Date:	Thu, 01 Nov 2012 19:53:00 +0000
From:	"Jan Beulich" <jbeulich@...e.com>
To:	<rostedt@...dmis.org>, <sqazi@...gle.com>
Cc:	<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

>>> 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.

Jan

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