Messages in this thread | | | Date | Fri, 8 Jun 2012 16:36:36 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge |
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On Fri, Jun 08, 2012 at 04:20:50PM +0200, Peter Zijlstra wrote: > On Fri, 2012-06-08 at 16:15 +0200, Borislav Petkov wrote: > > have a variable which gets initialized to the number of all CPUs and > > each time ->apply_microcode() finishes by returning 0, we decrement it > > once. > > > > > Hmm, I'm probably missing some obscure case. > > Since its all per-cpu sysfs muck, userspace could update a random > subsets of cpus.. leaving us hanging.
I'm afraid I don't understand - when you modprobe microcode.ko, it goes and loads /lib/firmware/amd-ucode/microcode_amd.bin (in the AMD case) on each CPU when the driver gets regged through subsys_interface_register().
It calls ->add_dev() on each CPU - this should be guaranteed because it uses the cpu_subsys from drivers/base/cpu.c which onlines all CPUs, I'd assume.
So, I'd say that once subsys_interface_register() returns, we have updated ucode on all CPUs, if successful...
We probably could run the notifier at that moment, before we do put_online_cpus().
> The 'bestestet' idea I came up with is doing the verify thing I have > from a delayed work -- say 1 second into the future. That way, when > there's lots of cpus they all try and enqueue the one work, which at > the end executes only once, provided the entire update scan took less > than the second.
You're saying, you want the last CPU that gets to update its microcode gets to also run the delayed work...? Probably, I'd assume ucode update on a single CPU takes less than a second IIUC.
-- Regards/Gruss, Boris.
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