Re: [Xen-devel] [PATCH v6 05/12] microcode: only save compatible ucode patches

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Mar 11, 2019 at 03:57:29PM +0800, Chao Gao wrote:
> Intel CPU only allows mixing in stepping or 'pf'. If an ucode patch is
> for other CPU families or models, it won't be compatible to all CPUs on
> current system and even hot-plugged CPUs.  Don't save such patch to
> reduce the size of ucode cache.

Oh, so we are indeed aiming to support systems that can require CPUs
to use different microcode blobs in order to update?

If that's the case, and we are sure this will work, we do indeed need
a list of microcodes, but you will have to somehow flag applied
microcodes in order to prevent them from being replaced with new
microcode versions until Xen knows that such new versions apply
correctly.

Maybe I'm being too simplistic here, but does anyone really have a
system with CPUs with different stepping?

Supporting such scenario adds quite a lot of complexity and even if
theoretically possible I don't think it makes much sense to support
unless there are such systems out there.

Thanks, Roger.

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