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bh=MayU9+vD4O6T4yz+K1BDfBsHfrw13iSYy4PwBql7Ftk=; b=VvR6wbfZs2gDuZifc1xRXEtCLdCAvH32T5G8zR2jOZgZrwjLdii2Fd4OMBcydJxDzGghlT du8Ho+sUKLJltCITSrzzMgQUV+N5BA927IDMiwtfTZPCvjePrznJ8po8D3CjUg4XaO/50i 0A5E8+SlagGRr0woWXVlW9ZqsIxo3QM= X-MC-Unique: T1J8J5EhP_KxIlDvDkANLA-1 From: Kevin Wolf To: qemu-block@nongnu.org Cc: kwolf@redhat.com, qemu-devel@nongnu.org Subject: [PULL 14/16] virtio: Re-enable notifications after drain Date: Wed, 7 Feb 2024 22:56:04 +0100 Message-ID: <20240207215606.206038-15-kwolf@redhat.com> In-Reply-To: <20240207215606.206038-1-kwolf@redhat.com> References: <20240207215606.206038-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.9 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.106, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1707343070185100001 Content-Type: text/plain; charset="utf-8" From: Hanna Czenczek During drain, we do not care about virtqueue notifications, which is why we remove the handlers on it. When removing those handlers, whether vq notifications are enabled or not depends on whether we were in polling mode or not; if not, they are enabled (by default); if so, they have been disabled by the io_poll_start callback. Because we do not care about those notifications after removing the handlers, this is fine. However, we have to explicitly ensure they are enabled when re-attaching the handlers, so we will resume receiving notifications. We do this in virtio_queue_aio_attach_host_notifier*(). If such a function is called while we are in a polling section, attaching the notifiers will then invoke the io_poll_start callback, re-disabling notifications. Because we will always miss virtqueue updates in the drained section, we also need to poll the virtqueue once after attaching the notifiers. Buglink: https://issues.redhat.com/browse/RHEL-3934 Signed-off-by: Hanna Czenczek Message-ID: <20240202153158.788922-3-hreitz@redhat.com> Reviewed-by: Stefan Hajnoczi Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf --- include/block/aio.h | 7 ++++++- hw/virtio/virtio.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 48 insertions(+), 1 deletion(-) diff --git a/include/block/aio.h b/include/block/aio.h index 5d0a114988..8378553eb9 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -480,9 +480,14 @@ void aio_set_event_notifier(AioContext *ctx, AioPollFn *io_poll, EventNotifierHandler *io_poll_ready); =20 -/* Set polling begin/end callbacks for an event notifier that has already = been +/* + * Set polling begin/end callbacks for an event notifier that has already = been * registered with aio_set_event_notifier. Do nothing if the event notifi= er is * not registered. + * + * Note that if the io_poll_end() callback (or the entire notifier) is rem= oved + * during polling, it will not be called, so an io_poll_begin() is not + * necessarily always followed by an io_poll_end(). */ void aio_set_event_notifier_poll(AioContext *ctx, EventNotifier *notifier, diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 7549094154..d229755eae 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -3556,6 +3556,17 @@ static void virtio_queue_host_notifier_aio_poll_end(= EventNotifier *n) =20 void virtio_queue_aio_attach_host_notifier(VirtQueue *vq, AioContext *ctx) { + /* + * virtio_queue_aio_detach_host_notifier() can leave notifications dis= abled. + * Re-enable them. (And if detach has not been used before, notificat= ions + * being enabled is still the default state while a notifier is attach= ed; + * see virtio_queue_host_notifier_aio_poll_end(), which will always le= ave + * notifications enabled once the polling section is left.) + */ + if (!virtio_queue_get_notification(vq)) { + virtio_queue_set_notification(vq, 1); + } + aio_set_event_notifier(ctx, &vq->host_notifier, virtio_queue_host_notifier_read, virtio_queue_host_notifier_aio_poll, @@ -3563,6 +3574,13 @@ void virtio_queue_aio_attach_host_notifier(VirtQueue= *vq, AioContext *ctx) aio_set_event_notifier_poll(ctx, &vq->host_notifier, virtio_queue_host_notifier_aio_poll_begin, virtio_queue_host_notifier_aio_poll_end); + + /* + * We will have ignored notifications about new requests from the guest + * while no notifiers were attached, so "kick" the virt queue to proce= ss + * those requests now. + */ + event_notifier_set(&vq->host_notifier); } =20 /* @@ -3573,14 +3591,38 @@ void virtio_queue_aio_attach_host_notifier(VirtQueu= e *vq, AioContext *ctx) */ void virtio_queue_aio_attach_host_notifier_no_poll(VirtQueue *vq, AioConte= xt *ctx) { + /* See virtio_queue_aio_attach_host_notifier() */ + if (!virtio_queue_get_notification(vq)) { + virtio_queue_set_notification(vq, 1); + } + aio_set_event_notifier(ctx, &vq->host_notifier, virtio_queue_host_notifier_read, NULL, NULL); + + /* + * See virtio_queue_aio_attach_host_notifier(). + * Note that this may be unnecessary for the type of virtqueues this + * function is used for. Still, it will not hurt to have a quick look= into + * whether we can/should process any of the virtqueue elements. + */ + event_notifier_set(&vq->host_notifier); } =20 void virtio_queue_aio_detach_host_notifier(VirtQueue *vq, AioContext *ctx) { aio_set_event_notifier(ctx, &vq->host_notifier, NULL, NULL, NULL); + + /* + * aio_set_event_notifier_poll() does not guarantee whether io_poll_en= d() + * will run after io_poll_begin(), so by removing the notifier, we do = not + * know whether virtio_queue_host_notifier_aio_poll_end() has run afte= r a + * previous virtio_queue_host_notifier_aio_poll_begin(), i.e. whether + * notifications are enabled or disabled. It does not really matter a= nyway; + * we just removed the notifier, so we do not care about notifications= until + * we potentially re-attach it. The attach_host_notifier functions wi= ll + * ensure that notifications are enabled again when they are needed. + */ } =20 void virtio_queue_host_notifier_read(EventNotifier *n) --=20 2.43.0