[Xen-changelog] [xen staging] x86/IRQ: don't keep EOI timer running without need

[patchbot@xxxxxxx]

commit 359cf6f8a0eccca3bd48624dbc8abd3da44dcf20
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jun 6 16:04:09 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jun 6 16:04:09 2019 +0200

    x86/IRQ: don't keep EOI timer running without need
    
    The timer needs to remain active only until all pending IRQ instances
    have seen EOIs from their respective domains. Stop it when the in-flight
    count has reached zero in desc_guest_eoi(). Note that this is race free
    (with __do_IRQ_guest()), as the IRQ descriptor lock is being held at
    that point.
    
    Also pull up stopping of the timer in __do_IRQ_guest() itself: Instead
    of stopping it immediately before re-setting, stop it as soon as we've
    made it past any early returns from the function (and hence we're sure
    it'll get set again).
    
    Finally bail from the actual timer handler in case we find the timer
    already active again by the time we've managed to acquire the IRQ
    descriptor lock. Without this we may forcibly EOI an IRQ immediately
    after it got sent to a guest. For this, timer_is_active() gets split out
    of active_timer(), deliberately moving just one of the two ASSERT()s (to
    allow the function to be used also on a never initialized timer).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/irq.c      | 17 ++++++++++++++++-
 xen/common/timer.c      |  5 ++---
 xen/include/xen/timer.h | 13 +++++++++++++
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index d6451a903b..335c8ffb67 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -1117,6 +1117,13 @@ static void irq_guest_eoi_timer_fn(void *data)
 
     action = (irq_guest_action_t *)desc->action;
 
+    /*
+     * Is another instance of this timer already running? Skip everything
+     * to avoid forcing an EOI early.
+     */
+    if ( timer_is_active(&action->eoi_timer) )
+        goto out;
+
     if ( action->ack_type != ACKTYPE_NONE )
     {
         unsigned int i;
@@ -1168,6 +1175,13 @@ static void __do_IRQ_guest(int irq)
         return;
     }
 
+    /*
+     * Stop the timer as soon as we're certain we'll set it again further down,
+     * to prevent the current timeout (if any) to needlessly expire.
+     */
+    if ( action->ack_type != ACKTYPE_NONE )
+        stop_timer(&action->eoi_timer);
+
     if ( action->ack_type == ACKTYPE_EOI )
     {
         sp = pending_eoi_sp(peoi);
@@ -1195,7 +1209,6 @@ static void __do_IRQ_guest(int irq)
 
     if ( action->ack_type != ACKTYPE_NONE )
     {
-        stop_timer(&action->eoi_timer);
         migrate_timer(&action->eoi_timer, smp_processor_id());
         set_timer(&action->eoi_timer, NOW() + MILLISECS(1));
     }
@@ -1458,6 +1471,8 @@ void desc_guest_eoi(struct irq_desc *desc, struct pirq 
*pirq)
         return;
     }
 
+    stop_timer(&action->eoi_timer);
+
     if ( action->ack_type == ACKTYPE_UNMASK )
     {
         ASSERT(cpumask_empty(action->cpu_eoi_map));
diff --git a/xen/common/timer.c b/xen/common/timer.c
index c85273bf82..80531d855d 100644
--- a/xen/common/timer.c
+++ b/xen/common/timer.c
@@ -282,11 +282,10 @@ static inline void timer_unlock(struct timer *timer)
 })
 
 
-static bool_t active_timer(struct timer *timer)
+static bool active_timer(const struct timer *timer)
 {
     ASSERT(timer->status >= TIMER_STATUS_inactive);
-    ASSERT(timer->status <= TIMER_STATUS_in_list);
-    return (timer->status >= TIMER_STATUS_in_heap);
+    return timer_is_active(timer);
 }
 
 
diff --git a/xen/include/xen/timer.h b/xen/include/xen/timer.h
index 4513260b0d..3a2a05c6de 100644
--- a/xen/include/xen/timer.h
+++ b/xen/include/xen/timer.h
@@ -75,6 +75,19 @@ bool timer_expires_before(struct timer *timer, s_time_t t);
 
 #define timer_is_expired(t) timer_expires_before(t, NOW())
 
+/*
+ * True if a timer is active.
+ *
+ * Unlike for timer_expires_before(), it is the caller's responsibility to
+ * use suitable locking such that the returned value isn't stale by the time
+ * it gets acted upon.
+ */
+static inline bool timer_is_active(const struct timer *timer)
+{
+    ASSERT(timer->status <= TIMER_STATUS_in_list);
+    return timer->status >= TIMER_STATUS_in_heap;
+}
+
 /* Migrate a timer to a different CPU. The timer may be currently active. */
 void migrate_timer(struct timer *timer, unsigned int new_cpu);
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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