linux-kernel - Re: 3.2.1 Unable to reset IRR messages on boot

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Message-ID: <20120320175423.GC30789@phenom.dumpdata.com>
Date:	Tue, 20 Mar 2012 13:54:23 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Josh Boyer <jwboyer@...hat.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	yinghai@...nel.org, linux-kernel@...r.kernel.org,
	kernel-team@...oraproject.org, midgoon@...il.com
Subject: Re: 3.2.1 Unable to reset IRR messages on boot

On Tue, Mar 20, 2012 at 10:59:24AM +0100, Ingo Molnar wrote:
> 
> * Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> 
> >  2). Make the Xen layer fake out an IOAPIC - so instead of 0xffffff, make sure to
> >      clear the three bits that Suresh' patch is testing for (Ewwwww, I don't actually
> >      like that - that stinks of a hack).
> 
> In what universe would a hardware virtualization layer emulating 
> actual hardware behavior be a 'hack'?

I think I didn't explain myself enough. The 2) "fix" would be basically the minimal work-around
around Suresh's patch so that the test his patch employs passes. That feels to me like a hack -
a band-aid solution. If his code employs more stringent tests in the next release, then I've got
to play catch-up and add more faking off the IOAPIC. That in long term might mean introducing
a pvops for the ioapic_read so that we can selectivity provide the "proper" IOAPIC entries.

The patch I posted thought tries to solve the existing baremetal problem Sureh's patch was for
and also not introduce a regression by only erasing the IOAPIC if there are no dependencies on it.
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