linux-kernel - Re: [PATCH] x86 microcode: work_on_cpu and cleanup of the synchronization logic

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Date:	Fri, 24 Apr 2009 19:00:31 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Dmitry Adamushko <dmitry.adamushko@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Peter Oruba <peter.oruba@....com>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86 microcode: work_on_cpu and cleanup of the 
 synchronization logic

On Fri, 24 Apr 2009, Dmitry Adamushko wrote:
> 2009/4/24 Dmitry Adamushko <dmitry.adamushko@...il.com>:
> > 2009/4/24 Hugh Dickins <hugh@...itas.com>:
> >>
> >> Good thinking, yes we can and do, unless I'm misinterpreting the
> >> evidence.  Though P4 Xeon and Atom startup messages give the opposite
> >> impression, claiming to update all cpus from lower revision, more
> >> careful tests starting from "maxcpus=1" and then "echo 1 >online"
> >> (which, unless you've fiddled around putting the microcode_ctl'ed
> >> microcode.dat into /lib/firmware/intel-ucode/wherever, isn't able
> >> to update at online time on Intel) shows that the later onlined
> >> siblings already have the updated microcode applied to their
> >> previously onlined siblings.  Which isn't surprising, but I'd
> >> been lulled into thinking the opposite by the startup sequence.
...
> 
> But then I wonder why behavior (the fact that all threads seem to
> upgrade to a newer version during the startup but they seem to already
> be 'up-to-date' if onlined later) during the startup is different...

I believe it's because the module_init microcode_init() calls
sysdev_driver_register(), which does mc_sysdev_add() of (all possible?)
cpus, which for online cpus calls microcode_init_cpu(), which does
collect_cpu_info() then, if SYSTEM_RUNNING, request_microcode_fw()
and apply_microcode_on_target() (names with your patch applied).

If the microcode driver is builtin (so gets here before SYSTEM_RUNNING),
or if it's for Intel with no firmware in /lib/firmware/intel-ucode/X-X-X
yet, the cpu_sig is thus obtained for all online cpus, before initscripts
run /sbin/microcode_ctl to update from /etc/microcode.dat successfully:
the "updated from revision" message shows uci->cpu_sig.rev as it
was saved earlier, rather than reevaluating it just before update.

That's confusing for us, and confusing when resume shows updated from
high revision to same high revision (though, I think, the revision
should in fact have reverted during suspend); but might be even more
worrying to HT users if it were corrected (it would seem as if only
half their cpus got updated, when before all were).  I don't know.

> Too pity that I can't see it with my setups (heh, I perhaps could play
> with it by actually downgrading cpus to older ucode).

Please, Intel, ship this man some out-of-date hardware!

(You're sure your cpus really are up-to-date?  I thought several
of my boxes were, but then discovered a modinfo line in openSUSE
11.1's /etc/init.d/microcode.ctl, which had been added since 10.3,
which was now disabling it when microcode driver built into kernel.)

Hugh
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