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

  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Fri, 20 Mar 2020 13:40:14 +0000
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  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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.

Would you be happy if I dropped just this aspect of the patch, and defer
AMD adjustments to a later set of changes?


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