Re: [Xen-devel] [PATCH v4 2/6] microcode: save all microcodes which pass sanity check

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.11.18 at 03:40, <chao.gao@xxxxxxxxx> wrote:
> On Wed, Nov 28, 2018 at 01:00:14PM +0100, Roger Pau Monné wrote:
>>On Wed, Nov 28, 2018 at 01:34:12PM +0800, Chao Gao wrote:
>>> @@ -491,6 +559,21 @@ static int cpu_request_microcode(unsigned int cpu, 
>>> const void *buf,
>>>      while ( (error = get_ucode_from_buffer_amd(mc_amd, buf, bufsize,
>>>                                                 &offset)) == 0 )
>>>      {
>>> +        struct ucode_patch *ucode_patch;
>>> +
>>> +        /*
>>> +         * Save this microcode before checking the signature. It is to
>>> +         * optimize microcode update on a mixed family system. Parsing
>>
>>Er, is it possible to have a system with CPUs of different family?
>>What's going to happen with CPUs having different features?
> 
> I have no idea. That each cpu has a per-cpu variable to store the
> microcode rather than a global one gives me a feeling that the current
> implementation wants to make it work on a system with CPUs of different
> family.

I think we've long given up on supporting mixed-model or even
mixed-family systems. Therefore in this overhaul doing away with
per-CPU tracking beyond the present ucode level (which indeed
may differ, even if we may have to consider to refuse keeping the
system up in such a case) would perhaps be pretty reasonable.

One thing definitely needs to work: Updating of ucode when
firmware has loaded differing versions (which usually boils down
to firmware neglecting to load ucode on all cores).

Jan


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