Re: [PATCH OSSTEST] Arrange to upgrade microcode on x86 test hosts.

[Ian Campbell <ian.campbell@citrix.com>]

On Thu, 2015-06-11 at 12:18 +0100, Jan Beulich wrote:
> >>> On 11.06.15 at 12:52, <ian.campbell@citrix.com> wrote:
> > Both Xen and Linux support extracting a microcode update from an
> > initramfs early during boot. This requires prepending a suitable
> > uncompressed cpio archive containing the necessary files to the
> > initrd.
> > 
> > Xen also supports loading the microcode cpio from any multiboot
> > module, but for in order to allow the possibility of loading on native
> > boots (e.g. for build jobs) we prefer the prepend method.
> > 
> > This patch provides mg-cpu-microcode-update which creates a suitable
> > microcode cpio in the images directory and arranges for it to be added
> > to the host during installation (so it is done before the kernel is
> > installed and initramfs generated etc, saving faff). It also adds
> > "ucode=scan" to the Xen command line when necessary.
> > 
> > The version of initramfs-tools in Wheezy does not yet support
> > prepending things to the initrm, so we use a custom compression
> > command which sneakily does it for us. This could be done better from
> > Jessie onwards.
> > 
> > Note that Linux only supports this from v3.8 onwards, so this doesn't
> > work for Wheezy (which uses v3.2). From Jessie onwards we should
> > benefit from microcode updates even for native (build) jobs.
> > 
> > Tested on both Intel and AMD where it appeared to have the desired
> > effect under Xen. Under native I only tried Wheezy which doesn't
> > support early microcode.
> > 
> > Note that I've not bothered to implement late microcode updates, which
> > would work on v3.2 too, since that would need a different set of files
> > etc and it doesn't seem especially pressing.
> > 
> > Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
> > Cc: Jan Beulich <JBeulich@suse.com>
> 
> Thanks for doing this so quickly, Ian!

No problem, it actually turned out to be easier than I had feared it
would be.

Ian.