linux-kernel - Re: [Xen-devel] [PATCH 1/4] xen/events: Clear cpu_evtchn

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Message-ID: <5541226D.3070501@oracle.com>
Date:	Wed, 29 Apr 2015 14:26:53 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>, konrad.wilk@...cle.com
CC:	xen-devel@...ts.xenproject.org, annie.li@...cle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH 1/4] xen/events: Clear cpu_evtchn_mask before
 resuming

On 04/29/2015 01:59 PM, David Vrabel wrote:
> On 29/04/15 17:54, Boris Ostrovsky wrote:
>> On 04/29/2015 12:32 PM, David Vrabel wrote:
>>> On 28/04/15 19:29, Boris Ostrovsky wrote:
>>>> On 04/28/2015 12:28 PM, David Vrabel wrote:
>>>>>    From the commit log the evtchn_2l_resume() fucntion that's added
>>>>> sounds
>>>>> like it fixes the problem on its own?
>>>> It in fact makes this problem worse since now that cpu_evtchn_mask is
>>>> cleared during resume we cannot process the interrupt anymore in
>>>> evtchn_2l_handle_events(): irqs have to be bound to a cpu in order for
>>>> an interrupt to be processed.
>>> Perhaps evtchn_2l_resume() should set the local cpu mask for any bound
>>> event channels? And then you wouldn't need IRQ_MOVE_PCNTX.
>> But then (at least in 2-level case) more than one VCPUs may pick the
>> same interrupt, won't they? Because the local cpu mask is what tells a
>> VCPU that it is allowed to claim an interrupt.
>
> We know that all event channels at this point are on VCPU0 (right?) so
> we only set the bit in that VCPU's mask.

This is pretty much what I was suggesting since setting the mask is done 
via bind_evtchn_to_cpu(). Except that I also want to call 
EVTCHNOP_bind_vcpu before that, just in case.

-boris
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