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Re: [Xen-devel] [PATCH v4 2/6] microcode: save all microcodes which pass sanity check
- To: Jan Beulich <JBeulich@xxxxxxxx>, Chao Gao <chao.gao@xxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 15 Jan 2019 15:07:07 +0000
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- Cc: Wei Liu <wei.liu2@xxxxxxxxxx>, Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Brian Woods <brian.woods@xxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Tue, 15 Jan 2019 15:11:27 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 30/11/2018 09:32, Jan Beulich wrote:
>>>> On 30.11.18 at 08:55, <chao.gao@xxxxxxxxx> wrote:
>> On Thu, Nov 29, 2018 at 10:22:10AM +0100, Roger Pau Monné wrote:
>>> On Thu, Nov 29, 2018 at 10:40:32AM +0800, Chao Gao 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:
>>>>>> ... and search caches to find a suitable one when loading.
>>>>> Why do you need to save all of them? You are only going to load a
>>>>> single microcode, so I don't understand the need to cache them all.
>>> I think the above question needs an answer.
>> Out of consideraton for a mixed-family system. Anyway, Since Jan commented
>> that we gave up support of a mixed-family system, we only need to save
>> a single microcode for offlined or hot-plugged cpus.
> Well, there might be slightly more needed than just a single instance.
> This depends on whether same family/model CPUs with different
> stepping and/or different "pf" value can be mixed (and would have
> identical feature flags in their CPUID output).
>
> I may have oversimplified the current state of things: Hotplugging
> a CPU with more capabilities than the boot CPU is generally fine
> afaict. Both you (Intel) and AMD place restrictions on permitted
> mixes iirc, so I don't think we need to support anything beyond
> such restrictions. Being able to run on permitted mixes which are
> not in conflict with our general assumption of there not being any
> CPU in the system with less capabilities than the boot CPU would
> seem desirable.
>
> Andrew, do you have any view or opinion here?
I'm not aware of anything since the P4 which has tolerated a
heterogeneous setup of physical CPUs.
Our current microcode loading doesn't support more than a single patch
per system, and I expect plenty of other things would break if we did
genuinely have a heterogeneous setup, featurewise.
I'd simplify everything and assume that there is only a single valid up
to date patch, and I doubt we'll see any problems.
~Andrew
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