| Message ID | 1486660298-11961-1-git-send-email-rcojocaru@bitdefender.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Feb 9, 2017 at 10:11 AM, Razvan Cojocaru <rcojocaru@bitdefender.com> wrote: > It is currently possible for the guest to lock when subscribing > to synchronous vm_events if max_vcpus is larger than the > number of available ring buffer slots. This patch no longer > blocks already paused VCPUs, fixing the issue for this use > case, and wakes up as many blocked VCPUs as there are slots > available in the ring buffer, eliminating the blockage for > asynchronous events. > > Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com> Acked-by: Tamas K Lengyel <tamas@tklengyel.com> > > --- > Changes since V2: > - Fixed typo: re-enabled commented-out code (for testing). > --- > xen/common/vm_event.c | 27 +++++++-------------------- > 1 file changed, 7 insertions(+), 20 deletions(-) > > diff --git a/xen/common/vm_event.c b/xen/common/vm_event.c > index 82ce8f1..45046d1 100644 > --- a/xen/common/vm_event.c > +++ b/xen/common/vm_event.c > @@ -127,26 +127,11 @@ static unsigned int vm_event_ring_available(struct vm_event_domain *ved) > static void vm_event_wake_blocked(struct domain *d, struct vm_event_domain *ved) > { > struct vcpu *v; > - int online = d->max_vcpus; > unsigned int avail_req = vm_event_ring_available(ved); > > if ( avail_req == 0 || ved->blocked == 0 ) > return; > > - /* > - * We ensure that we only have vCPUs online if there are enough free slots > - * for their memory events to be processed. This will ensure that no > - * memory events are lost (due to the fact that certain types of events > - * cannot be replayed, we need to ensure that there is space in the ring > - * for when they are hit). > - * See comment below in vm_event_put_request(). > - */ > - for_each_vcpu ( d, v ) > - if ( test_bit(ved->pause_flag, &v->pause_flags) ) > - online--; > - > - ASSERT(online == (d->max_vcpus - ved->blocked)); > - > /* We remember which vcpu last woke up to avoid scanning always linearly > * from zero and starving higher-numbered vcpus under high load */ > if ( d->vcpu ) > @@ -160,13 +145,13 @@ static void vm_event_wake_blocked(struct domain *d, struct vm_event_domain *ved) > if ( !v ) > continue; > > - if ( !(ved->blocked) || online >= avail_req ) > + if ( !(ved->blocked) || avail_req == 0 ) > break; > > if ( test_and_clear_bit(ved->pause_flag, &v->pause_flags) ) > { > vcpu_unpause(v); > - online++; > + avail_req--; > ved->blocked--; > ved->last_vcpu_wake_up = k; > } > @@ -280,8 +265,9 @@ void vm_event_put_request(struct domain *d, > int free_req; > unsigned int avail_req; > RING_IDX req_prod; > + struct vcpu *curr = current; > > - if ( current->domain != d ) > + if ( curr->domain != d ) > { > req->flags |= VM_EVENT_FLAG_FOREIGN; > #ifndef NDEBUG > @@ -316,8 +302,9 @@ void vm_event_put_request(struct domain *d, > * See the comments above wake_blocked() for more information > * on how this mechanism works to avoid waiting. */ > avail_req = vm_event_ring_available(ved); > - if( current->domain == d && avail_req < d->max_vcpus ) > - vm_event_mark_and_pause(current, ved); > + if( curr->domain == d && avail_req < d->max_vcpus && > + !atomic_read(&curr->vm_event_pause_count) ) > + vm_event_mark_and_pause(curr, ved); > > vm_event_ring_unlock(ved); > > -- > 1.9.1 > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > https://lists.xen.org/xen-devel
diff --git a/xen/common/vm_event.c b/xen/common/vm_event.c index 82ce8f1..45046d1 100644 --- a/xen/common/vm_event.c +++ b/xen/common/vm_event.c @@ -127,26 +127,11 @@ static unsigned int vm_event_ring_available(struct vm_event_domain *ved) static void vm_event_wake_blocked(struct domain *d, struct vm_event_domain *ved) { struct vcpu *v; - int online = d->max_vcpus; unsigned int avail_req = vm_event_ring_available(ved); if ( avail_req == 0 || ved->blocked == 0 ) return; - /* - * We ensure that we only have vCPUs online if there are enough free slots - * for their memory events to be processed. This will ensure that no - * memory events are lost (due to the fact that certain types of events - * cannot be replayed, we need to ensure that there is space in the ring - * for when they are hit). - * See comment below in vm_event_put_request(). - */ - for_each_vcpu ( d, v ) - if ( test_bit(ved->pause_flag, &v->pause_flags) ) - online--; - - ASSERT(online == (d->max_vcpus - ved->blocked)); - /* We remember which vcpu last woke up to avoid scanning always linearly * from zero and starving higher-numbered vcpus under high load */ if ( d->vcpu ) @@ -160,13 +145,13 @@ static void vm_event_wake_blocked(struct domain *d, struct vm_event_domain *ved) if ( !v ) continue; - if ( !(ved->blocked) || online >= avail_req ) + if ( !(ved->blocked) || avail_req == 0 ) break; if ( test_and_clear_bit(ved->pause_flag, &v->pause_flags) ) { vcpu_unpause(v); - online++; + avail_req--; ved->blocked--; ved->last_vcpu_wake_up = k; } @@ -280,8 +265,9 @@ void vm_event_put_request(struct domain *d, int free_req; unsigned int avail_req; RING_IDX req_prod; + struct vcpu *curr = current; - if ( current->domain != d ) + if ( curr->domain != d ) { req->flags |= VM_EVENT_FLAG_FOREIGN; #ifndef NDEBUG @@ -316,8 +302,9 @@ void vm_event_put_request(struct domain *d, * See the comments above wake_blocked() for more information * on how this mechanism works to avoid waiting. */ avail_req = vm_event_ring_available(ved); - if( current->domain == d && avail_req < d->max_vcpus ) - vm_event_mark_and_pause(current, ved); + if( curr->domain == d && avail_req < d->max_vcpus && + !atomic_read(&curr->vm_event_pause_count) ) + vm_event_mark_and_pause(curr, ved); vm_event_ring_unlock(ved);
It is currently possible for the guest to lock when subscribing to synchronous vm_events if max_vcpus is larger than the number of available ring buffer slots. This patch no longer blocks already paused VCPUs, fixing the issue for this use case, and wakes up as many blocked VCPUs as there are slots available in the ring buffer, eliminating the blockage for asynchronous events. Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com> --- Changes since V2: - Fixed typo: re-enabled commented-out code (for testing). --- xen/common/vm_event.c | 27 +++++++-------------------- 1 file changed, 7 insertions(+), 20 deletions(-)