From: Lin Ming Subject: Re: Unsigned widening casts of binary "not" operations.. Date: Thu, 25 Apr 2013 09:13:38 +0800 Message-ID: References: <20130424072630.GB1780@gmail.com> <20130424074735.GB1751@moon> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: Ingo Molnar , Linus Torvalds , Peter Zijlstra , "H. Peter Anvin" , Thomas Gleixner , David Miller , "Theodore Ts'o" , Linux Kernel Mailing List , "the arch/x86 maintainers" , Network Development , "linux-ext4@vger.kernel.org" , Oleg Nesterov , Frederic Weisbecker To: Cyrill Gorcunov Return-path: Received: from mail-lb0-f182.google.com ([209.85.217.182]:44533 "EHLO mail-lb0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758658Ab3DYBNk (ORCPT ); Wed, 24 Apr 2013 21:13:40 -0400 In-Reply-To: <20130424074735.GB1751@moon> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, Apr 24, 2013 at 3:47 PM, Cyrill Gorcunov wrote: > On Wed, Apr 24, 2013 at 09:26:30AM +0200, Ingo Molnar wrote: >> >> * Linus Torvalds 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 > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html