xen/events: defer eoi in case of excessive number of events

In case rogue guests are sending events at high frequency it might
happen that xen_evtchn_do_upcall() won't stop processing events in
dom0. As this is done in irq handling a crash might be the result.

In order to avoid that, delay further inter-domain events after some
time in xen_evtchn_do_upcall() by forcing eoi processing into a
worker on the same cpu, thus inhibiting new events coming in.

The time after which eoi processing is to be delayed is configurable
via a new module parameter "event_loop_timeout" which specifies the
maximum event loop time in jiffies (default: 2, the value was chosen
after some tests showing that a value of 2 was the lowest with an
only slight drop of dom0 network throughput while multiple guests
performed an event storm).

How long eoi processing will be delayed can be specified via another
parameter "event_eoi_delay" (again in jiffies, default 10, again the
value was chosen after testing with different delay values).

This is part of XSA-332.

Cc: stable@vger.kernel.org
Reported-by: Julien Grall <julien@xen.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Wei Liu <wl@xen.org>

1 files changed, 11 insertions, 19 deletions

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 40e4ca1685aa..6085a808da95 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -275,19 +275,9 @@ static uint32_t clear_linked(volatile event_word_t *word)
 	return w & EVTCHN_FIFO_LINK_MASK;
 }
 
-static void handle_irq_for_port(evtchn_port_t port)
-{
-	int irq;
-
-	irq = get_evtchn_to_irq(port);
-	if (irq != -1)
-		generic_handle_irq(irq);
-}
-
-static void consume_one_event(unsigned cpu,
+static void consume_one_event(unsigned cpu, struct evtchn_loop_ctrl *ctrl,
 			      struct evtchn_fifo_control_block *control_block,
-			      unsigned priority, unsigned long *ready,
-			      bool drop)
+			      unsigned priority, unsigned long *ready)
 {
 	struct evtchn_fifo_queue *q = &per_cpu(cpu_queue, cpu);
 	uint32_t head;
@@ -320,16 +310,17 @@ static void consume_one_event(unsigned cpu,
 		clear_bit(priority, ready);
 
 	if (evtchn_fifo_is_pending(port) && !evtchn_fifo_is_masked(port)) {
-		if (unlikely(drop))
+		if (unlikely(!ctrl))
 			pr_warn("Dropping pending event for port %u\n", port);
 		else
-			handle_irq_for_port(port);
+			handle_irq_for_port(port, ctrl);
 	}
 
 	q->head[priority] = head;
 }
 
-static void __evtchn_fifo_handle_events(unsigned cpu, bool drop)
+static void __evtchn_fifo_handle_events(unsigned cpu,
+					struct evtchn_loop_ctrl *ctrl)
 {
 	struct evtchn_fifo_control_block *control_block;
 	unsigned long ready;
@@ -341,14 +332,15 @@ static void __evtchn_fifo_handle_events(unsigned cpu, bool drop)
 
 	while (ready) {
 		q = find_first_bit(&ready, EVTCHN_FIFO_MAX_QUEUES);
-		consume_one_event(cpu, control_block, q, &ready, drop);
+		consume_one_event(cpu, ctrl, control_block, q, &ready);
 		ready |= xchg(&control_block->ready, 0);
 	}
 }
 
-static void evtchn_fifo_handle_events(unsigned cpu)
+static void evtchn_fifo_handle_events(unsigned cpu,
+				      struct evtchn_loop_ctrl *ctrl)
 {
-	__evtchn_fifo_handle_events(cpu, false);
+	__evtchn_fifo_handle_events(cpu, ctrl);
 }
 
 static void evtchn_fifo_resume(void)
@@ -416,7 +408,7 @@ static int evtchn_fifo_percpu_init(unsigned int cpu)
 
 static int evtchn_fifo_percpu_deinit(unsigned int cpu)
 {
-	__evtchn_fifo_handle_events(cpu, true);
+	__evtchn_fifo_handle_events(cpu, NULL);
 	return 0;
 }