Re: Current state of Xen microcode (Was: Re: uploading 3.16~rc5-1~exp1)

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Jul 23, 2014 at 03:59:37PM +0100, Jan Beulich wrote:
> >>> On 15.07.14 at 16:59, <konrad.wilk@oracle.com> wrote:
> > On Tue, Jul 15, 2014 at 09:53:32AM +0100, Ian Campbell wrote:
> >> Adding xen-devel and some of the Linux maints,
> >> 
> >> On Mon, 2014-07-14 at 23:22 +0200, maximilian attems wrote:
> >> > I will upload tomorrow Tuesday around 22h00 UT to experimental.
> >> > 
> >> > There are two TODOS concerning the not yet forwarded Debian patches:
> >> > - cgroups
> >> > - xen microcode
> >> > 
> >> > 
> >> > I consider both not a blocker, but would be happy if Xen guys could
> >> > have a look for what is needed.
> >> 
> >> The xen microcode patches which maks is referring to are these:
> >> 
> > http://anonscm.debian.org/viewvc/kernel/dists/trunk/linux/debian/patches/feat 
> > ures/all/xen/
> >> which are a forward port of Jeremy's old microcode_xen.ko driver.
> > 
> > They are also at my branch
> > http://git.kernel.org/cgit/linux/kernel/git/konrad/xen.git/log/?h=stable/mis 
> > c
> > 
> > Hm, I should rebase them at some point.
> >> 
> >> I've not been keeping up on Xen x86 microcode stuff these days but I
> >> think we don't need this any more with modern Xen since we can parse the
> >> microcode blob off the front of the initrd, is that right?
> > 
> > Right. And best of it, the support for that is in dracut so
> > it automatically can happen (thought you still need to add
> > 'ucode=scan' in the /etc/default/grub.cfg in the GRUB_CMDLINE_XEN
> > parameter) and also in /etc/dracut.conf add 'early_microcode=yes'.
> 
> Except that all this still doesn't take care of updating microcode at
> runtime. Yet that should - like kexec - be implemented in the
> respective tools such that no kernel involvement it required.

What are such tools? My recollection is that it is matter of
sticking the files in /lib/firmware and then udev - will try
at the detection of an CPU becoming online, do:
 - load microcode module
 - echo 1 > to the 'reload' sysfs parameter

Perhaps the solution is simple:
 - write an xen userspace tool that will do this loading via
   the hypercalls.
 - plug said tool in the udev script that comes with xen.
 - distros will install said udev scripts when they install Xen rpms?

That sounds too simple to be true. I must be missing something :-)
> 
> Jan
>