Re: [PATCH] x86, amd_ucode: Skip microcode updates for final levels

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 31/07/2015 21:45, Aravind Gopalakrishnan wrote:
> On 7/30/2015 12:01 PM, Andrew Cooper wrote:
>> On 30/07/15 17:23, Aravind Gopalakrishnan wrote:
>>> Some of older[Fam10h] systems require that the microcode versions
>>> that it comes up with should not be updated by the microcode driver.
>>> Otherwise, system hangs are known to occur.
>>>
>>> In this patch, we check for those microcode versions and abort the
>>> update process if existing microcode level is already applied by
>>> the BIOS.
>>>
>>> A linux version of the patch has already made it into tip-
>>> http://marc.info/?l=linux-kernel&m=143703405627170
>>>
>>> Signed-off-by: Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>
>>> ---
>>>   xen/arch/x86/microcode_amd.c | 31 +++++++++++++++++++++++++++++++
>>>   1 file changed, 31 insertions(+)
>>>
>>> diff --git a/xen/arch/x86/microcode_amd.c
>>> b/xen/arch/x86/microcode_amd.c
>>> index f79b397..c958a47 100644
>>> --- a/xen/arch/x86/microcode_amd.c
>>> +++ b/xen/arch/x86/microcode_amd.c
>>> @@ -347,6 +347,30 @@ static int container_fast_forward(const void
>>> *data, size_t size_left, size_t *of
>>>       return 0;
>>>   }
>>>   
>> Please include the same comment as the Linux patch, explaining that
>> these microcode versions can't be updated from.
>
> Ok, will do that.
>
>> I would also like to see some documentation from AMD concerning this.
>
> (hopefully) answering Boris' question too here-
>
> So, the patch id values have only been obtained empirically.
> The Linux patch provides the bug reference for
> this:https://bugzilla.suse.com/show_bug.cgi?id=913996
> (It's a fairly long thread but the gist of it is that people
> predominantly seem to be experiencing system hang issues
> when they try to update microcode levels from these patch ids:
> 0x01000098,  0x0100009f, 0x010000af)
>
> From discussing about it internally, we gathered that OS/hypervisor
> cannot reliably perform microcode updates beyond these specified levels
> due to HW issues.

Ok - please include this information in the comment as well please.

~Andrew