linux-kernel - Re: [PATCH 0/2] Fix dmar fault interrupt problems

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Date:	Tue, 30 Nov 2010 11:52:41 -0800
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"indou.takao@...fujitsu.com" <indou.takao@...fujitsu.com>
Subject: Re: [PATCH 0/2] Fix dmar fault interrupt problems

On Tue, 2010-11-30 at 11:28 -0800, Chris Wright wrote:
> AFAICT, it just becomes a duplicate call in a narrow window.
> 
> native_smp_prepare_cpus() (or APIC_init_uniprocessor()):
>  enable_IR_x2apic()
>   enable_IR()
>    enable_intr_remapping() <-- clears faults
>  default_setup_apic_routing()
>    enable_drhd_fault_handling() <-- added call to clear faults
> 
> That's what I meant by not needed.

I agree that we will call clear faults twice.

With out the second clear fault, any fault in that narrow window of
enabling intr-remapping and enabling fault handling will go unnoticed
and block further faults getting reported.

I am not sure if the first fault is necessary. I can check and remove it
if not needed.

Ideally we want to do something like:

Setup fault handling
Clear any faults
Enable intr-remapping

But fault handling interrupt configuration depends on the apic mode that
gets selected based on whether intr-remapping was enabled successfully
or not. And hence we were enabling fault handling after enabling the
intr-remapping mode.

I can see if I can cleanup any of these flows for 2.6.38. For 2.6.37 and
older kernels I would like to keep the patch simple.

thanks,
suresh

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