Re: [PATCH for-4.14] docs/ucode: Extend runtime microcode loading documentation

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jun 01, 2020 at 02:40:25PM +0100, Andrew Cooper wrote:
> Extend the disclaimer about runtime loading.  While we've done our best to
> make the mechaism reliable, the safety of late loading does ultimately depend
> on the contents of the blobs.
> 
> Extend the xen-ucode portion with examples of how to use it.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

> ---
> CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Wei Liu <wl@xxxxxxx>
> CC: Julien Grall <julien@xxxxxxx>
> CC: Paul Durrant <paul@xxxxxxx>
> ---
>  docs/admin-guide/microcode-loading.rst | 22 +++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/docs/admin-guide/microcode-loading.rst 
> b/docs/admin-guide/microcode-loading.rst
> index 5f0f661a2e..8cd5d0351b 100644
> --- a/docs/admin-guide/microcode-loading.rst
> +++ b/docs/admin-guide/microcode-loading.rst
> @@ -104,8 +104,8 @@ modules to find any CPIO archives, and search the archive 
> for the applicable
>  file.  Xen will stop searching at the first match.
>  
>  
> -Run time microcode loading
> ---------------------------
> +Runtime microcode loading
> +-------------------------
>  
>  .. warning::
>  
> @@ -113,7 +113,23 @@ Run time microcode loading
>     or at boot time.  Not all microcode updates (or parts thereof) can be
>     applied at runtime.
>  
> -The ``xen-ucode`` utility can be used to initiate a runtime microcode load.
> +   Given the proprietry nature of microcode, we are unable to make any claim
> +   that a runtime microcode is risk-free.  Any runtime microcode loading 
> needs
> +   adequate testing on a dev instance before being rolled out to production
> +   systems.
> +
> +The ``xen-ucode`` utility can be used to initiate a runtime microcode load::
> +
> +  [root@host ~]# xen-ucode
> +  xen-ucode: Xen microcode updating tool
> +  Usage: xen-ucode <microcode blob>
> +  [root@host ~]#
> +
> +e.g. With a Linux dom0 on a Haswell system::
> +
> +  [root@host ~]# xen-ucode /lib/firmware/intel-ucode/06-3c-03

Could you expand a bit on the nomenclature used here?

I assume it's something like <fam>-<model>-<version> but might be good
to provide people a hint to know how to find the appropriate blob for
their system if possible.

Thanks, Roger.