From c3049fad2b01e85e944d928763f2b012eebf080e Mon Sep 17 00:00:00 2001 From: David Vrabel Date: Tue, 15 Dec 2015 15:55:23 +0100 Subject: [PATCH] evtchn: don't reuse ports that are still "busy" When using the FIFO ABI a guest may close an event channel that is still LINKED. If this port is reused, subsequent events may be lost because they may become pending on the wrong queue. This could be fixed by requiring guests to only close event channels that are not linked. This is difficult since: a) irq cleanup in the guest may be done in a context that cannot wait for the event to be unlinked; b) the guest may attempt to rebind a PIRQ whose previous close is still pending; and c) existing guests already have the problematic behaviour. Instead, simply check a port is not "busy" (i.e., it's not linked) before reusing it. Guests should still drain any queues for VCPUs that are being offlined, or the port will become unusable until the VCPU is onlined and starts processing events again. Signed-off-by: David Vrabel Reviewed-by: Jan Beulich master commit: 78e24c269b0a4a8b864ece725e6d4209ed95dfa7 master date: 2015-12-02 15:21:46 +0100 --- xen/common/event_channel.c | 3 ++- xen/common/event_fifo.c | 12 ++++++++++++ xen/include/xen/event.h | 12 ++++++++++++ 3 files changed, 26 insertions(+), 1 deletion(-) diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c index 2774cbba16..0e4c1953d6 100644 --- a/xen/common/event_channel.c +++ b/xen/common/event_channel.c @@ -171,7 +171,8 @@ static int get_free_port(struct domain *d) { if ( port > d->max_evtchn_port ) return -ENOSPC; - if ( evtchn_from_port(d, port)->state == ECS_FREE ) + if ( evtchn_from_port(d, port)->state == ECS_FREE + && !evtchn_port_is_busy(d, port) ) return port; } diff --git a/xen/common/event_fifo.c b/xen/common/event_fifo.c index e9c1fbe4d5..a443c98018 100644 --- a/xen/common/event_fifo.c +++ b/xen/common/event_fifo.c @@ -313,6 +313,17 @@ static bool_t evtchn_fifo_is_masked(struct domain *d, return test_bit(EVTCHN_FIFO_MASKED, word); } +static bool_t evtchn_fifo_is_busy(struct domain *d, evtchn_port_t port) +{ + event_word_t *word; + + word = evtchn_fifo_word_from_port(d, port); + if ( unlikely(!word) ) + return 0; + + return test_bit(EVTCHN_FIFO_LINKED, word); +} + static int evtchn_fifo_set_priority(struct domain *d, struct evtchn *evtchn, unsigned int priority) { @@ -352,6 +363,7 @@ static const struct evtchn_port_ops evtchn_port_ops_fifo = .unmask = evtchn_fifo_unmask, .is_pending = evtchn_fifo_is_pending, .is_masked = evtchn_fifo_is_masked, + .is_busy = evtchn_fifo_is_busy, .set_priority = evtchn_fifo_set_priority, .print_state = evtchn_fifo_print_state, }; diff --git a/xen/include/xen/event.h b/xen/include/xen/event.h index 06c0654fa6..075f4da451 100644 --- a/xen/include/xen/event.h +++ b/xen/include/xen/event.h @@ -138,6 +138,11 @@ struct evtchn_port_ops { void (*unmask)(struct domain *d, struct evtchn *evtchn); bool_t (*is_pending)(struct domain *d, const struct evtchn *evtchn); bool_t (*is_masked)(struct domain *d, const struct evtchn *evtchn); + /* + * Is the port unavailable because it's still being cleaned up + * after being closed? + */ + bool_t (*is_busy)(struct domain *d, evtchn_port_t port); int (*set_priority)(struct domain *d, struct evtchn *evtchn, unsigned int priority); void (*print_state)(struct domain *d, const struct evtchn *evtchn); @@ -179,6 +184,13 @@ static inline bool_t evtchn_port_is_masked(struct domain *d, return d->evtchn_port_ops->is_masked(d, evtchn); } +static inline bool_t evtchn_port_is_busy(struct domain *d, evtchn_port_t port) +{ + if ( d->evtchn_port_ops->is_busy ) + return d->evtchn_port_ops->is_busy(d, port); + return 0; +} + static inline int evtchn_port_set_priority(struct domain *d, struct evtchn *evtchn, unsigned int priority)