From: "Liang, Kan" <kan.liang@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>
CC: "mingo@redhat.com" <mingo@redhat.com>,
        "acme@kernel.org" <acme@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "eranian@google.com" <eranian@google.com>,
        "jolsa@kernel.org" <jolsa@kernel.org>,
        "ak@linux.intel.com" <ak@linux.intel.com>
Subject: RE: [PATCH 1/3] perf/x86: add sysfs entry to freeze counter on SMI
Thread-Topic: [PATCH 1/3] perf/x86: add sysfs entry to freeze counter on SMI
Thread-Index: AQHSpARyOIb5UUisk0KlFjSvZGKZaKGiWyiAgADIv4CAAOFrYA==
Date: Fri, 24 Mar 2017 14:15:16 +0000
Message-ID: <37D7C6CF3E00A74B8858931C1DB2F077536C3CCB@SHSMSX103.ccr.corp.intel.com>
References: <1490293551-5552-1-git-send-email-kan.liang@intel.com>
 <1490293551-5552-2-git-send-email-kan.liang@intel.com>
 <20170323203255.kps67homffxhl3cv@hirez.programming.kicks-ass.net>
 <alpine.DEB.2.20.1703240929030.3688@nanos>
In-Reply-To: <alpine.DEB.2.20.1703240929030.3688@nanos>
Accept-Language: zh-CN, en-US
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Content-Transfer-Encoding: 8bit
Content-Length: 900
Lines: 28


> On Thu, 23 Mar 2017, Peter Zijlstra wrote:
> > On Thu, Mar 23, 2017 at 11:25:49AM -0700, kan.liang@intel.com wrote:
> > > +	for_each_possible_cpu(cpu) {
> > > +		rdmsrl_on_cpu(cpu, MSR_IA32_DEBUGCTLMSR,
> &debugctlmsr);
> > > +		if (val)
> > > +			wrmsrl_on_cpu(cpu, MSR_IA32_DEBUGCTLMSR,
> debugctlmsr | DEBUGCTLMSR_FREEZE_WHILE_SMM);
> > > +		else
> > > +			wrmsrl_on_cpu(cpu, MSR_IA32_DEBUGCTLMSR,
> debugctlmsr & ~DEBUGCTLMSR_FREEZE_WHILE_SMM);
> > > +	}
> >
> > No; that's just disgusting. Also {rd,wr}msr_on_cpu() should die,
> > exactly because people end up writing crap like this.
> 
> Aside of that this is completely broken against other users of
> DEBUGCTLMSR because it's not atomic vs. the other modifications.
> 

OK. I will change it.
I guess I need a way/function which can atomically rd,wr msr on all cpus.
Are there existing alternative ways/functions to do that?

Thanks,
Kan