Messages in this thread | | | Subject | Re: [PATCH -v2 1/2] x86, microcode: Sanitize per-cpu microcode reloading interface | From | Peter Zijlstra <> | Date | Thu, 21 Jun 2012 14:12:22 +0200 |
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On Thu, 2012-06-21 at 14:07 +0200, Borislav Petkov wrote: > From: Borislav Petkov <borislav.petkov@amd.com> > > Microcode reloading in a per-core manner is a very bad idea for both > major x86 vendors. And the thing is, we have such interface with which > we can end up with different microcode versions applied on different > cores of an otherwise homogeneous wrt (family,model,stepping) system. > > So turn off the possibility of doing that per core and allow it only > system-wide. > > This is a minimal fix which we'd like to see in stable too thus the > more-or-less arbitrary decision to allow system-wide reloading only on > the BSP: > > $ echo 1 > /sys/devices/system/cpu/cpu0/microcode/reload > ... > > and disable the interface on the other cores: > > $ echo 1 > /sys/devices/system/cpu/cpu23/microcode/reload > -bash: echo: write error: Invalid argument > > Also, allowing the reload only from one CPU (the BSP in > that case) doesn't allow the reload procedure to degenerate > into an O(n^2) deal when triggering reloads from all > /sys/devices/system/cpu/cpuX/microcode/reload sysfs nodes > simultaneously. > > A more generic fix will follow. > > Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br> Acked-by: Peter Zijlstra <peterz@infradead.org>
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