Re: [Xen-devel] [PATCH V4 2/2] x86, amd_ucode: Skip microcode updates for final levels

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.08.15 at 21:11, <aravind.gopalakrishnan@xxxxxxx> wrote:
> Some of older[Fam10h] systems require that certain number of
> applied microcode patch levels should not be overwritten by
> the microcode loader. Otherwise, system hangs are known to occur.
> 
> The 'final_levels' of patch ids have been obtained empirically.
> Refer bug https://bugzilla.suse.com/show_bug.cgi?id=913996 
> for details of the issue.
> 
> The short version is that people have predominantly noticed
> system hang issues when trying to update microcode levels
> beyond the patch IDs below.
> [0x01000098, 0x0100009f, 0x010000af]
> 
> From internal discussions, we gathered that OS/hypervisor
> cannot reliably perform microcode updates beyond these levels
> due to hardware issues. Therefore, we need to abort microcode
> update process if we hit any of these levels.

While the patch itself looks fine now, I'm still hesitant to take this
(even more so after having read through the bugzilla entry
linked to above): The list being established empirically - will it be
ever growing? Did you internally gain understanding of what it
actually is that goes wrong (and hence can perhaps narrow
down the conditions for the hangs to occur)? Have there been
any checks whether indeed _all_ systems at the listed ucode
levels are affected?

Also that's leaving aside the question of what unfixed CPU issues
people now being prevented from doing the ucode update are
going to run into.

Jan


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