From: Jan Beulich <jbeulich@suse.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Ian Jackson <iwj@xenproject.org>, Julien Grall <julien@xen.org>,
Wei Liu <wl@xen.org>, Stefano Stabellini <sstabellini@kernel.org>
Subject: [PATCH v5 6/6] evtchn: drop acquiring of per-channel lock from send_guest_{global,vcpu}_virq()
Date: Wed, 27 Jan 2021 09:17:42 +0100 [thread overview]
Message-ID: <5c3e705a-d028-dc9e-0f22-cb2e55f250f7@suse.com> (raw)
In-Reply-To: <306e62e8-9070-2db9-c959-858465c50c1d@suse.com>
The per-vCPU virq_lock, which is being held anyway, together with there
not being any call to evtchn_port_set_pending() when v->virq_to_evtchn[]
is zero, provide sufficient guarantees. Undo the lock addition done for
XSA-343 (commit e045199c7c9c "evtchn: address races with
evtchn_reset()"). Update the description next to struct evtchn_port_ops
accordingly.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v4: Move to end of series, for being the most controversial change.
v3: Re-base.
v2: New.
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -812,7 +812,6 @@ void send_guest_vcpu_virq(struct vcpu *v
unsigned long flags;
int port;
struct domain *d;
- struct evtchn *chn;
ASSERT(!virq_is_global(virq));
@@ -823,12 +822,7 @@ void send_guest_vcpu_virq(struct vcpu *v
goto out;
d = v->domain;
- chn = evtchn_from_port(d, port);
- if ( evtchn_read_trylock(chn) )
- {
- evtchn_port_set_pending(d, v->vcpu_id, chn);
- evtchn_read_unlock(chn);
- }
+ evtchn_port_set_pending(d, v->vcpu_id, evtchn_from_port(d, port));
out:
read_unlock_irqrestore(&v->virq_lock, flags);
@@ -857,11 +851,7 @@ void send_guest_global_virq(struct domai
goto out;
chn = evtchn_from_port(d, port);
- if ( evtchn_read_trylock(chn) )
- {
- evtchn_port_set_pending(d, chn->notify_vcpu_id, chn);
- evtchn_read_unlock(chn);
- }
+ evtchn_port_set_pending(d, chn->notify_vcpu_id, chn);
out:
read_unlock_irqrestore(&v->virq_lock, flags);
--- a/xen/include/xen/event.h
+++ b/xen/include/xen/event.h
@@ -193,9 +193,16 @@ int evtchn_reset(struct domain *d, bool
* Low-level event channel port ops.
*
* All hooks have to be called with a lock held which prevents the channel
- * from changing state. This may be the domain event lock, the per-channel
- * lock, or in the case of sending interdomain events also the other side's
- * per-channel lock. Exceptions apply in certain cases for the PV shim.
+ * from changing state. This may be
+ * - the domain event lock,
+ * - the per-channel lock,
+ * - in the case of sending interdomain events the other side's per-channel
+ * lock,
+ * - in the case of sending non-global vIRQ-s the per-vCPU virq_lock (in
+ * combination with the ordering enforced through how the vCPU's
+ * virq_to_evtchn[] gets updated),
+ * - in the case of sending global vIRQ-s vCPU 0's virq_lock.
+ * Exceptions apply in certain cases for the PV shim.
*/
struct evtchn_port_ops {
void (*init)(struct domain *d, struct evtchn *evtchn);
next prev parent reply other threads:[~2021-01-27 8:17 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-27 8:13 [PATCH v5 0/6] evtchn: (not so) recent XSAs follow-on Jan Beulich
2021-01-27 8:15 ` [PATCH v5 1/6] evtchn: use per-channel lock where possible Jan Beulich
2021-01-27 8:16 ` [PATCH v5 2/6] evtchn: convert domain event lock to an r/w one Jan Beulich
2021-05-27 11:01 ` Roger Pau Monné
2021-05-27 11:16 ` Jan Beulich
2022-07-07 18:00 ` Julien Grall
2021-01-27 8:16 ` [PATCH v5 3/6] evtchn: slightly defer lock acquire where possible Jan Beulich
2021-01-27 8:16 ` [PATCH v5 4/6] evtchn: add helper for port_is_valid() + evtchn_from_port() Jan Beulich
2021-01-27 8:17 ` [PATCH v5 5/6] evtchn: type adjustments Jan Beulich
2021-01-27 8:17 ` Jan Beulich [this message]
2021-04-21 15:23 ` Ping: [PATCH v5 0/6] evtchn: (not so) recent XSAs follow-on Jan Beulich
2021-04-21 15:56 ` Julien Grall
2021-04-22 8:53 ` Jan Beulich
2021-05-14 15:29 ` Roger Pau Monné
2021-05-17 7:15 ` Jan Beulich
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