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    SubjectRe: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge
    On Wed, Jun 13, 2012 at 09:36:49AM -0300, Henrique de Moraes Holschuh wrote:
    > Yes, please. I suggest we use core 0 for that. Using my Debian
    > maintainer hat, I'd rather you got rid of the sysfs entries for every
    > other core while at it, as it will make our life a lot simpler,
    > distro-side.

    Wouldn't we have some sort of ABI breakage if I remove the sysfs files?
    Instead, I was thinking of having the rest of the files not on the BSP
    return -EINVAL and only the BSP reload ucode on the whole system.

    > This is still not the proper fix, which would be to add a new sysfs node
    > to access the proper update-every-core functionality, but it is a damn
    > good start in the right direction and required to make it safe without
    > ripping out the old ABI entirely without a deprecation period.

    Yes, I'd like to have the system-wide sysfs node somewhere under
    /sys/devices/system/cpu/microcode/ but we'll see how that goes.

    > Since Intel processors don't want the per-core behaviour either, you
    > could fix it in the microcode core itself...


    > Ok. Please CC me in the patches, if the new ABI arrives in time, I'll
    > even be able to get it supported on the next Debian stable (and push
    > to get this stuff backported to the kernel 3.2 which we will ship,
    > I consider this an important bug-fix to a pontentially very serious
    > issue. We have *zero* chance of finding out what's wrong if an users'
    > system start getting subtly crazy because it is running with skewed
    > microcode among cores.

    Ok, will do.

    Btw, I have to think about whether we really want to backport this to
    stable since it is not a regression fix but functionality change which
    kinda fixes a some sort of bug. Hmm, the stable rules are kinda blurry
    here. I could write a minimal fix with stable in mind though... we'll

    hpa, what is our take here, should we backport a minimal change
    disabling reloading of ucode per-cpu for stable? It is the wrong thing
    to do anyway.


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