Re: [Xen-devel] Linux 3.11 and the future...

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.06.13 at 15:07, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> On Thu, Jun 06, 2013 at 08:38:57AM +0100, Jan Beulich wrote:
>> >>> On 05.06.13 at 22:19, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
>> >>> wrote:
>> >  b) microcode update. One needs to cherry-pick
>> >     xen: add CPU microcode update driver
>> >     x86/microcode: check proper return code.
>> >     microcode_xen: Add support for AMD family >= 15h
>> > 
>> >    The one solution is to use the piggyback on early microcode loading
>> >    that the Linux kernel is doing. Needs implementation in the hypervisor.
>> 
>> What hypervisor side solution apart from the existing ucode
>> updating during early boot are you thinking of here?
> 
> Copy from the
> http://wiki.xen.org/wiki/GSoC_2013#Microcode_uploader_implementation_in_Xen_ 
> hypervisor
> 
> "
> Intel is working on early implementation where the microcode binary
> would be appended to the initrd image. The kernel would scan for the
> appropriate magic constant
> (http://thread.gmane.org/gmane.linux.kernel/1413384; looks for
> "kernel/x86/microcode/GenuineIntel.bin") and load the microcode very
> early. This is all done for the Linux kernel code, but we currently do
> not that in the Xen hypervisor.
> The scope of the work can be split up in
> a) just do the extraction of microcode from the initial ramdisk binary (aka
> initrd) and apply it. This can be done during the parsing of the dom0
> initial ramdisk. The hypervisor already has the functionality to apply a
> microcode from the multiboot targets. This would add code to parse the
> initrd image
> b) do it during very early bootup - which is why the early microcode work
> started - to deal with CPUs which don't expose certain CPUID flags
> because they need a microcode update. This part of work is much more
> difficult - as it would involve working only with early bootup
> pagetables. This being done _before_ the Xen hypervisor sets its own
> pagetables - as some of the fixes that the microcode has, can be for the
> CPU to be able to do PSE properly.
> "
> 
> The a) solution was what I had in mind.

Imo this is not a viable option - we shouldn't start peeking into the
second module (which Linux uses as initrd, but which other OSes
may use for other purposes) - so far this is just a binary blob to the
hypervisor.

Jan


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