linux-kernel - Re: [PATCH v3] enable x2APIC without interrupt remapping under KVM

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Date:	Wed, 01 Jul 2009 15:53:28 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Avi Kivity <avi@...hat.com>, Gleb Natapov <gleb@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sheng Yang <sheng@...ux.intel.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, garyhade@...ibm.com
Subject: Re: [PATCH v3] enable x2APIC without interrupt remapping under KVM

On Tue, 2009-06-30 at 12:36 -0700, Eric W. Biederman wrote:
> Dropped irqs..  Driver hangs because it is waiting for an irq.  Hardware
> hangs because it is waiting for the cpu to process the irq.
> 
> Potentially we get a level triggered irq that is never acked by
> the cpu that won't arm until the cpu send an ack, and we can't
> send an ack from another cpu.

Eric,

Among number of experiments you have tried in the past to fix this, have
you tried the experiment of explicitly clearing the remoteIRR by
changing the trigger mode to edge and then back to level.

Is there a problem with this?

We can send a spurious IPI (after the RTE migration) with the new vector
to another cpu and handler which services the level interrupt will check
if we saw the edge mode for a level interrupt and then the handler can
explicitly restore the level trigger and reset the remote IRR by mask
+edge and unmask+level.

We might have to work with some rough edges but do you recollect any
major issue with this approach..

thanks,
suresh

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