Re: [PATCH] microcode: Scan the multiboot payloads for cpio format microcode blob. (v3.3)

[Keir Fraser <keir.xen@gmail.com>]

Acked-by: Keir Fraser <keir@xen.org>

On 27/09/2013 02:09, "Konrad Rzeszutek Wilk" <konrad@kernel.org> wrote:

> <blurb from v1>:
> Please see the following patch which implements a mechanism to scan
> the initramfs for the format of an microcode files. This is a feature
> that the Linux kernel has since v3.10 - where it searches in the
> initramfs for an archive of the microcode blob. The format is documented
> in the Linux tree and the commit description contains it.
> 
> The tool to make this work is the initramfs creator. The one tool
> 'dracut' has support for this via the '--early-microcode' parameter.
> (See http://news.gmane.org/gmane.linux.kernel.initramfs for dracut 030
> announcement))
> 
> That, along with this patch, allows the Xen hypervisor to update the
> microcode during bootup. Please review attached patch.
> 
> I had also tested just using Linux how well it deals with an initramfs
> composed of two cpio images. Testing revealed that it worked great
> even if the kernel did not have the early cpio support build in.
> David Vrabel pointed out that it b/c:
> "The kernel unpacks all cpio archives it finds in the initramfs image so
> the kernel doesn't have to be aware of the way tools have packed the
> filesystem into different cpio archive."
> 
> The way to use this is by the 'ucode' parameter. It has now two meanings:
>   [<index>|initrd]
> 
> Which CANNOT be used together. By default this auto scanning is turned off
> as Jan pointed out that: "Xen otoh has to be careful not to
> mis-interpret a blob passed to a non-Linux Dom0 as a CPIO. How
> good the guarding against this is in the code I'll have to check".
> 
> The author would like to have this on by default but that can wait
> till a later time when maintainer is comfortable with this being
> on by default.
> </blurb from v1>
> 
> There is also the question whether the parameter should be 'cpio','initrd'
> or 'scan'. As in the future the extraction of the payload could be from
> a different format than the cpio (say a microcode blob with an magic
> string at the start). The author believes that at that time the logic
> to scan the mulitboot payloads can be expanded to also scan formats other
> than cpio format. Jan (who initially raised this question) in the last review
> did not comment on the choice so I think it is left to Keir (if he cares about
> the distinction).
> 
> Please apply!
> 
>  docs/misc/xen-command-line.markdown |   14 ++-
>  xen/arch/x86/microcode.c            |  175 +++++++++++++++++++++++++++++++---
>  xen/common/Makefile                 |    2 +-
>  xen/common/earlycpio.c              |  151 ++++++++++++++++++++++++++++++
>  xen/include/xen/earlycpio.h         |   14 +++
>  5 files changed, 336 insertions(+), 20 deletions(-)
> 
> Konrad Rzeszutek Wilk (2):
>       microcode: Scan the initramfs payload for microcode blob.
>       microcode: Check whether the microcode is correct.
>