Message-ID: <4FD7A99F.8030007@zytor.com>
Date: Tue, 12 Jun 2012 13:42:07 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1
MIME-Version: 1.0
To: Borislav Petkov <bp@amd64.org>
CC: Peter Zijlstra <peterz@infradead.org>,
        Stephane Eranian <eranian@google.com>, linux-kernel@vger.kernel.org,
        andi@firstfloor.org, mingo@elte.hu, ming.m.lin@intel.com,
        "Yu, Fenghua" <fenghua.yu@intel.com>
Subject: Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge
References: <20120607071531.GA4849@quad> <4FD78BE6.4060207@zytor.com> <20120612190720.GA11137@aftab.osrc.amd.com> <1339529614.31548.104.camel@twins> <20120612194900.GC11137@aftab.osrc.amd.com> <4FD7A687.3040500@zytor.com> <20120612203730.GE11137@aftab.osrc.amd.com>
In-Reply-To: <20120612203730.GE11137@aftab.osrc.amd.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1431
Lines: 35

On 06/12/2012 01:37 PM, Borislav Petkov wrote:
> On Tue, Jun 12, 2012 at 01:28:55PM -0700, H. Peter Anvin wrote:
>> On 06/12/2012 12:49 PM, Borislav Petkov wrote:
>>>
>>> Also, I'd assume we need some of the current functionality to be able to
>>> load ucode without rebooting the box.
>>>
>>
>> Yes, the basic idea is that we'll keep the ucode around anyway so we can
>> feed it to hotplug CPUs or S3 resume.  If the ucode is updated from
>> userspace we'd replace the in-memory copy and load it into the CPUs.
> 
> You say CPUs, i.e. plural. What is your take on loading ucode on a
> single core, i.e. the /sys/devices/system/cpu/cpuX/microcode/reload
> interface? Do you guys need to load ucode only system-wide or can you
> stomach per-core loads?
> 
> I want to disable it (or even remove it, modulo the whole userspace
> compat blah blah) on AMD.
> 
> Also, if we do system-wide, can we have a single sysfs node where we
> give the new ucode from userspace instead of per-cpu files?
> 

I personally don't know of any valid use case for per-core loads, and it
sounds like a horrid idea.  And yes, I would prefer a single sysfs file,
or better yet a plain old device node.

	-hpa

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/