Re: [Xen-devel] [PATCH 7/7] x86/ucode/intel: Fold structures together

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/03/2020 12:24, Jan Beulich wrote:
> On 25.03.2020 15:32, Andrew Cooper wrote:
>> On 25/03/2020 14:16, Jan Beulich wrote:
>>> On 23.03.2020 11:17, Andrew Cooper wrote:
>>>> Currently, we allocate an 8 byte struct microcode_patch to point at a
>>>> separately allocated struct microcode_intel.  This is wasteful.
>>> As indicated elsewhere I'm very much in favor of this, but I think it
>>> wants doing in one of the earlier series, and then for AMD at the same
>>> time.
>> I've got some ideas for an AMD series given the replies I got, and will
>> be able to do an equivalent microcode_amd => microcode_patch folding on
>> that side.  There is also further work to do, including unbreaking the
>> OSVW logic (which has been totally clobbered by the start/end_update
>> debacle).
>>
>> However, given that it taken this whole series to make the transition
>> look safe on the Intel side, I really don't see a way of doing this
>> "earlier".
>>
>> In particular, no amount of ifdefary suggested below can AFAICT make it
>> safe to do this transform without having microcode_patch opaque to being
>> with.
>>
>> Yes - there is a bit of churn, but I can't see a safe alternative.
> Something like the one below (compile tested only, and not really
> cleaned up in any way)?
>
> Jan

Thanks.  I'll experiment with this approach.

On a perhaps tangential note, what (if anything) are you plans regarding
backport here?

These defines are ok for a transitional period across a series (and
probably means I'll need to get the AMD side ready to be committed at
the same time), but I don't think we'd want them in the code for the
longterm.

I personally wasn't overly concerned about backports, but if you are, we
should probably take this into consideration for the fixes.

~Andrew