Re: [PATCH] perf/x86: check ucode before disabling PEBS onSandyBridge

[Borislav Petkov]

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?

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