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openSUSE:Leap:15.4:Update
xen.23693
5fbcdf2e-evtchn-FIFO-access-last.patch
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File 5fbcdf2e-evtchn-FIFO-access-last.patch of Package xen.23693
# Commit 1277cb9dc5e966f1faf665bcded02b7533e38078 # Date 2020-11-24 11:23:42 +0100 # Author Juergen Gross <jgross@suse.com> # Committer Jan Beulich <jbeulich@suse.com> xen/events: access last_priority and last_vcpu_id together The queue for a fifo event is depending on the vcpu_id and the priority of the event. When sending an event it might happen the event needs to change queues and the old queue needs to be kept for keeping the links between queue elements intact. For this purpose the event channel contains last_priority and last_vcpu_id values elements for being able to identify the old queue. In order to avoid races always access last_priority and last_vcpu_id with a single atomic operation avoiding any inconsistencies. Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Julien Grall <jgrall@amazon.com> --- a/xen/common/event_fifo.c +++ b/xen/common/event_fifo.c @@ -21,6 +21,14 @@ #include <public/event_channel.h> +union evtchn_fifo_lastq { + uint32_t raw; + struct { + uint8_t last_priority; + uint16_t last_vcpu_id; + }; +}; + static inline event_word_t *evtchn_fifo_word_from_port(const struct domain *d, unsigned int port) { @@ -64,16 +72,18 @@ static struct evtchn_fifo_queue *lock_ol struct vcpu *v; struct evtchn_fifo_queue *q, *old_q; unsigned int try; + union evtchn_fifo_lastq lastq; for ( try = 0; try < 3; try++ ) { - v = d->vcpu[evtchn->last_vcpu_id]; - old_q = &v->evtchn_fifo->queue[evtchn->last_priority]; + lastq.raw = read_atomic(&evtchn->fifo_lastq); + v = d->vcpu[lastq.last_vcpu_id]; + old_q = &v->evtchn_fifo->queue[lastq.last_priority]; spin_lock_irqsave(&old_q->lock, *flags); - v = d->vcpu[evtchn->last_vcpu_id]; - q = &v->evtchn_fifo->queue[evtchn->last_priority]; + v = d->vcpu[lastq.last_vcpu_id]; + q = &v->evtchn_fifo->queue[lastq.last_priority]; if ( old_q == q ) return old_q; @@ -224,8 +234,11 @@ static void evtchn_fifo_set_pending(stru /* Moved to a different queue? */ if ( old_q != q ) { - evtchn->last_vcpu_id = v->vcpu_id; - evtchn->last_priority = q->priority; + union evtchn_fifo_lastq lastq = { }; + + lastq.last_vcpu_id = v->vcpu_id; + lastq.last_priority = q->priority; + write_atomic(&evtchn->fifo_lastq, lastq.raw); spin_unlock_irqrestore(&old_q->lock, flags); spin_lock_irqsave(&q->lock, flags); --- a/xen/include/xen/sched.h +++ b/xen/include/xen/sched.h @@ -113,8 +113,7 @@ struct evtchn #ifndef NDEBUG u8 old_state; /* State when taking lock in write mode. */ #endif - u8 last_priority; - u16 last_vcpu_id; + u32 fifo_lastq; /* Data for fifo events identifying last queue. */ #ifdef CONFIG_XSM union { #ifdef XSM_NEED_GENERIC_EVTCHN_SSID
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