linux-kernel - Re: [RFC -tip] x86,apic: set cpu_has

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Message-ID: <20090819161500.GA5457@lenovo>
Date:	Wed, 19 Aug 2009 20:15:00 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC -tip] x86,apic: set cpu_has_apic manually for discrete
	apic

[Cyrill Gorcunov - Sun, Aug 16, 2009 at 11:57:36PM +0400]
|
| In case of discrete apic (due to hardware or firmware reason)
| cpuid may not retrieve cpu_has_apic bit. But we rely on this
| bit in SMP compiled kernels. So instead of long condition checking
| we set cpu_has_apic bit manually and check it only in further
| code flow.
| 
| Note that the case is applied to x86-32 pretty old machines only.
| Also verify_local_APIC is the only place where such a trick
| could be done. We can't do it earlier since there could be
| a BIOS bug and other checks which we are to pass to ensure
| that APIC is functional.
| 
| The patch also make lapic_shutdown, disable_IO_APIC callable
| which should take place even on discrete apics.
| 
| As a side effect it makes lapic sysfs device available
| for such machines so lets check for apic being integrated
| since we don't support suspend/resume for disrete apics.
| 
| Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
| ---

Please drop this RFC now as to eliminate side effects
a number of quirks (MCE,MSI) would be needed. I didn't trigger
problems because not all interrupt types were covered
with qemu. The simpliest (and more safe) approach will
be just to fix lapic_shutdown and disable_IO_APIC for
discrete apic case. Will cook a patch.

	-- Cyrill
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