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

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Date:	Fri, 24 Apr 2009 00:16:35 +0200
From:	Dmitry Adamushko <dmitry.adamushko@...il.com>
To:	Hugh Dickins <hugh@...itas.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

2009/4/23 Hugh Dickins <hugh@...itas.com>:
> On Thu, 23 Apr 2009, Dmitry Adamushko wrote:
>> [ ... ]
>> - change update_match_revision() in microcode_intel.c in a way that
>> allows loading of a ucode with a revision == the current revision
>> (rev. 0x57 in my case). From the POV of the microcode module it
>> nevertheless looks like an update;
>
> My P4 Xeon and Core2s and Atom all want newer microcode from the
> latest microcode.dat, and your version seems to work fine on them.

Thanks for the tests and review!

> [ ... ]
>
> That SYSTEM_RUNNING test you've flagged with "--dimm. Review this case":
> yes, that's still necessary for when CONFIG_MICROCODE=y (and no initrd?),
> as I have - trying to get the firmware at that point will hang.  I did
> try changing module_init(microcode_init) to late_initcall(microcode_init),
> but that didn't solve it.  And skipping out at that point does leave CPU0
> not updated.  But you've not made anything worse there, and most people
> will have CONFIG_MICROCODE=m.

Yeah. Then at least for the sake of consistency it makes sense to
consider doing some kind of delayed update for CPU0 in this case. Will
check.

>>
>> p.s. argh... just noticed that the following line is redundant in
>> microcode_core.c (forgot to remove it)
>>
>> +enum { UCODE_UPDATE_ERR, UCODE_UPDATE_OK, UCODE_UPDATE_NAVAIL };
>
> A couple of things that worried me.
>
> I guess your mutex Synchronization works out, but are interrupts
> still disabled around the critical wrmsr()s, wherever they're getting
> called from?

Yes, *msr() calls are only done from functions that are now being
called via smp_call_function_single(). The later seems to always do it
with disabled interrupts. The only exception is mc_sysdev_resume()
calling  ->apply_microcode() directly but this one in turn is always
called with disabled interrupts.

But now that you mentioned it I wonder if we may actually need a
spinlock there... can we have multi-threaded cpus/cores with (all |
some) shared msr registers?


> And you've a habit of returning -1 in error cases, which later gets
> muddled in with errnos, so that it would amount to -EPERM, which is
> probably not what you want.

Indeed, will fix. Thanks!


>
> Hugh
>

-- 
Best regards,
Dmitry Adamushko
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