linux-ext4 - Re: Unsigned widening casts of binary "not" operations..

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Date:	Wed, 24 Apr 2013 11:47:35 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Miller <davem@...emloft.net>,
	Theodore Ts'o <tytso@....edu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Lin Ming <ming.m.lin@...el.com>
Subject: Re: Unsigned widening casts of binary "not" operations..

On Wed, Apr 24, 2013 at 09:26:30AM +0200, Ingo Molnar wrote:
> 
> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > And there's quite a lot of them. Even in my (fairly small) config I use on
> > my desktop. And the first warnings I see are in x86 code:
> > 
> >     arch/x86/kernel/traps.c:405:16: warning: implicit unsigned widening
> > cast of a '~' expression
> >     arch/x86/kernel/cpu/perf_event_p4.c:912:15: warning: implicit unsigned
> > widening cast of a '~' expression
> 
> Hm, the perf_event_p4.c code is indeed confused.
> 
> I think the bug is real but probably benign in effect: we allow narrower 
> values into the MSR register than probably intended. Only a couple of low 
> bits are reserved AFAICS.
> 
> Here's an (untested!) patch that tries to untangle it all: it just moves 
> to clean 64-bit types everywhere - these MSRs are 64-bit wide regardless 
> of whether we run on 32-bit or not.
> 
> Would be nice if someone with a working P4 could test it - Cyrill? [It 
> should also be double checked whether the high words are really not 
> reserved and can be written to ...]

Hi Ingo! Ufortunately I don't have access to real p4 hardware,
thus I'm CC'ing Ming who has been helping a lot in testing
this code pieces.

Still the patch itself is perfectly fine to me

Reviewed-by: Cyrill Gorcunov <gorcunov@...nvz.org>
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