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Re: [Xen-devel] [PATCH 4/6] x86/ucode: Rationalise startup and family/model checks

On 20.03.2020 15:27, Andrew Cooper wrote:
> On 20/03/2020 13:56, Jan Beulich wrote:
>> On 20.03.2020 14:40, Andrew Cooper wrote:
>>> On 20/03/2020 13:37, Jan Beulich wrote:
>>>> On 19.03.2020 16:26, Andrew Cooper wrote:
>>>>> Drop microcode_init_{intel,amd}(), export {intel,amd}_ucode_ops, and use a
>>>>> switch statement in early_microcode_init() rather than probing each 
>>>>> vendor in
>>>>> turn.  This allows the microcode_ops pointer to become local to core.c.
>>>>> As there are no external users of microcode_ops, there is no need for
>>>>> collect_cpu_info() to implement sanity checks.  Move applicable checks to
>>>>> early_microcode_init() so they are performed once, rather than repeatedly.
>>>>> Items to note:
>>>>>  * The AMD ucode driver does have an upper familiy limit of 0x17, as a 
>>>>> side
>>>>>    effect of the logic in verify_patch_size() which does need updating for
>>>>>    each new model.
>>>> I don't see this being the case, and hence I think it is this patch
>>>> which introduces such a restriction. As long a patches are less
>>>> than 2k, all unspecified families are supported by verify_patch_size()
>>>> through its default: case label. (Arguably the name F1XH_MPB_MAX_SIZE
>>>> doesn't really fit how it is being used.)
>>>> I'm happy about all other changes made here.
>>> Linux actually has a different algorithm which drops length restrictions
>>> on Fam15h and later, so they get forward compatibility that way.
>> If that's what AMD mandates/suggests, we {c,sh}ould consider doing
>> so too. I thought though that these length restrictions were actually
>> put in by AMD folks.
> Its on the list of questions...
>>> Would you be happy if I dropped just this aspect of the patch, and defer
>>> AMD adjustments to a later set of changes?
>> Yes, as said - everything else looked good to me.
> Can I take that as an A-by then, to save posting the patch again?

If it's just taking out the fam <= 0x17 check - yes.


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