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

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Message-ID: <CAF1ivSbO7RBB_CoS7wXWHQVkz2sw4kYKaz00dU2YziRxe0arVg@mail.gmail.com>
Date:	Thu, 25 Apr 2013 09:13:38 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	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>
Subject: Re: Unsigned widening casts of binary "not" operations..

On Wed, Apr 24, 2013 at 3:47 PM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> 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.

Hi,

Sorry, but I don't have access to p4 hardware either.

Lin Ming

>
> Still the patch itself is perfectly fine to me
>
> Reviewed-by: Cyrill Gorcunov <gorcunov@...nvz.org>
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