Re: [patch 0/4] x86: AMD microcode patch loading v2 fixes

[Peter Oruba]

Max Krasnyansky schrieb:
> Dmitry Adamushko wrote:
> > 2008/7/29 Peter Oruba <peter.oruba@xxxxxxx>:
> > > Fixed coding style issues.
> >
> > I have a comment on the abstraction layer (microcode_ops).
> >
> > [ Not that I've looked very carefully at it so far, nor I pretend to
> > be at-ease with this 'microcode' topic to make any design judgements
> > :-) ]
> >
> > but would it be somehow possible to not have set_cpus_allowed_ptr()
> > code in arch-dependent parts? Let's say the mechanism of how to run
> > certain arch-specific code (and synchronization) on a given cpu should
> > be a prerogative of (and placed in) the generic part...
> >
> > Note, this code will likely happily give you an oops if you run
> > cpu_down/up() ;-)
> >
> > I also wondered, is there a requirement that when a new cpu is brought
> > up, microcode updates {should,must} be done as early as possible, say
> > before any tasks have a chance to run on it? Or can the update be a
> > bit delayed? e.g. we don't do it from cpu-hotplug handlers.
>
> Dmitry looks like you missed my email. I already asked that question and 
> proposed a couple of options (workqueue and ipi).
> Tigran said that he does not know. Maybe Peter does.
>
> My guess is that it does not have to be done synchronously and can be 
> delayed. There is no guaranty that microcode CPU hotplug handler will 
> run before all the other handlers. Which by definition means that some 
> things will start running on the cpu before the microcode is updated. 
> Hence we might as well do the update outside of the cpu hotplug path.
>
> Max

Since ucode updates may fix severe issues, it is supposed to happen as early as 
possible. If you re-plug your CPU into your socket, your BIOS also applies a 
ucode patch, but that won't necessarily be the latest and critical one.

Peter

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