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

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Date:	Tue, 28 Apr 2015 11:52:10 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	david.vrabel@...rix.com, konrad.wilk@...cle.com
Cc:	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	annie.li@...cle.com, boris.ostrovsky@...cle.com
Subject: [PATCH 1/4] xen/events: Clear cpu_evtchn_mask before resuming

When a guest is resumed, the hypervisor may change event channel
assignments. If this happens and the guest uses 2-level events it
is possible for the interrupt to be claimed by wrong VCPU since
cpu_evtchn_mask bits may be stale. This can happen even though
evtchn_2l_bind_to_cpu() attempts to clear old bits: irq_info that
is passed in is not necessarily the original one (from pre-migration
times) but instead is freshly allocated during resume and so any
information about which CPU the channel was bound to is lost.

Thus we should clear the mask during resume.

We also need to make sure that bits for xenstore and console channels
are set when these two subsystems are resumed. While rebind_evtchn_irq()
(which is invoked for both of them on a resume) calls irq_set_affinity(),
the latter will in fact postpone setting affinity until handling the
interrupt. But because cpu_evtchn_mask will have bits for these two cleared
we won't be able to take the interrupt.

Setting IRQ_MOVE_PCNTXT flag for the two irqs avoids this problem by
allowing to set affinity immediately, which is safe for event-channel-based
interrupts.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Reported-by: Annie Li <annie.li@...cle.com>
Tested-by: Annie Li <annie.li@...cle.com>
---
 drivers/tty/hvc/hvc_xen.c         |    1 +
 drivers/xen/events/events_2l.c    |   10 ++++++++++
 drivers/xen/xenbus/xenbus_comms.c |    1 +
 3 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
index f1e5742..5eb80bd 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -533,6 +533,7 @@ static int __init xen_hvc_init(void)

 		info = vtermno_to_xencons(HVC_COOKIE);
 		info->irq = bind_evtchn_to_irq(info->evtchn);
+		irq_set_status_flags(info->irq, IRQ_MOVE_PCNTXT);
 	}
 	if (info->irq < 0)
 		info->irq = 0; /* NO_IRQ */
diff --git a/drivers/xen/events/events_2l.c b/drivers/xen/events/events_2l.c
index 5db43fc..7dd4631 100644
--- a/drivers/xen/events/events_2l.c
+++ b/drivers/xen/events/events_2l.c
@@ -345,6 +345,15 @@ irqreturn_t xen_debug_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }

+static void evtchn_2l_resume(void)
+{
+	int i;
+
+	for_each_online_cpu(i)
+		memset(per_cpu(cpu_evtchn_mask, i), 0, sizeof(xen_ulong_t) *
+				EVTCHN_2L_NR_CHANNELS/BITS_PER_EVTCHN_WORD);
+}
+
 static const struct evtchn_ops evtchn_ops_2l = {
 	.max_channels      = evtchn_2l_max_channels,
 	.nr_channels       = evtchn_2l_max_channels,
@@ -356,6 +365,7 @@ static const struct evtchn_ops evtchn_ops_2l = {
 	.mask              = evtchn_2l_mask,
 	.unmask            = evtchn_2l_unmask,
 	.handle_events     = evtchn_2l_handle_events,
+	.resume	           = evtchn_2l_resume,
 };

 void __init xen_evtchn_2l_init(void)
diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
index fdb0f33..30203d1 100644
--- a/drivers/xen/xenbus/xenbus_comms.c
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -231,6 +231,7 @@ int xb_init_comms(void)
 		}

 		xenbus_irq = err;
+		irq_set_status_flags(xenbus_irq, IRQ_MOVE_PCNTXT);
 	}

 	return 0;
-- 
1.7.1

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