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Re: ANNOUNCEMENT: Intel/AMD x86 CPU microcode update system in non-free

On Tue, 06 Nov 2012, Erwan David wrote:
> On Mon, Nov 05, 2012 at 09:12:53PM CET, Henrique de Moraes Holschuh <hmh@debian.org> said:
> > Microcode updates will be applied immediately when the microcode
> > packages are installed or updated: you don't have to reboot.  You will
> > have to keep the packages installed, though: as explained above, the
> > microcode updates have to be reapplied at every boot.
> >
> > You can check which version of the microcode your processors are running
> > by looking for "microcode" lines on /proc/cpuinfo.  This information is
> > only available on recent kernels (such as the Wheezy kernel).
> One minor point : on two machines I had to reboot in order for the new
> microcode to be applied. Maybe because I installed iucode-tool in the
> same aptitude invocation, thus it was not fully instead at time of
> intel-microcode post-install ?

AFAIK, this can happen if you update the packages for the *running* kernel
beforehand (without a reboot) or at the same dpkg/apt/synaptic invocation as
you installed {amd64,intel}-microcode, *and* you did't have the required
"microcode" module loaded beforehand.

When that happens, by the time {amd64,intel}-microcode can tell the system
to load the microcode module, it is too late: the module file present in the
system will be for the updated kernel, and will likely refuse to load until
you reboot to load the new kernel.  This is exactly the situation the kernel
packages will have warned you about durihg in-place kernel upgrades: you
need to reboot.

iucode_tool is not used to load the microcode, but it is used to reduce
*greatly* the amount of space the Intel microcode will take up inside the
initramfs (this can be tweaked/disabled in /etc/default/intel-microcode),
but it will only work if it can access the "cpuid" functionality, which also
requires loading some modules to work.

If you had the kernel-update issue, you might want to manually run
"update-initramfs -u" as root once, just in case.

In any case, you will only have the above problems when installing the
packages.  After that, the microcode module will be loaded anyway by the
initramfs (so they will always be able to update the microcode), and a
script will be added to /etc/kernel/preinst.d by intel-microcode to make
sure iucode_tool will have access to "cpuid" on during future kernel

AMD processors don't need something like iucode_tool because the AMD
microcode update data files are very small.

  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

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