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140 lines
6.0 KiB
140 lines
6.0 KiB
From 2a758da4e1433564998def68447008908c96e113 Mon Sep 17 00:00:00 2001
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From: Hanna Czenczek <hreitz@redhat.com>
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Date: Fri, 2 Feb 2024 16:31:57 +0100
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Subject: [PATCH 2/6] virtio: Re-enable notifications after drain
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RH-Author: Hanna Czenczek <hreitz@redhat.com>
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RH-MergeRequest: 223: virtio: Re-enable notifications after drain
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RH-Jira: RHEL-3934
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Commit: [2/3] e3be798e6259a378fc03f4364ecaeb875b01f64c (hreitz/qemu-kvm-c-9-s)
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During drain, we do not care about virtqueue notifications, which is why
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we remove the handlers on it. When removing those handlers, whether vq
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notifications are enabled or not depends on whether we were in polling
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mode or not; if not, they are enabled (by default); if so, they have
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been disabled by the io_poll_start callback.
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Because we do not care about those notifications after removing the
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handlers, this is fine. However, we have to explicitly ensure they are
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enabled when re-attaching the handlers, so we will resume receiving
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notifications. We do this in virtio_queue_aio_attach_host_notifier*().
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If such a function is called while we are in a polling section,
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attaching the notifiers will then invoke the io_poll_start callback,
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re-disabling notifications.
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Because we will always miss virtqueue updates in the drained section, we
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also need to poll the virtqueue once after attaching the notifiers.
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Buglink: https://issues.redhat.com/browse/RHEL-3934
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Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
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Message-ID: <20240202153158.788922-3-hreitz@redhat.com>
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Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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Reviewed-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit 5bdbaebcce18fe6a627cafad2043ec08f3de5744)
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---
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hw/virtio/virtio.c | 42 ++++++++++++++++++++++++++++++++++++++++++
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include/block/aio.h | 7 ++++++-
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2 files changed, 48 insertions(+), 1 deletion(-)
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diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
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index 3a160f86ed..356d690cc9 100644
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--- a/hw/virtio/virtio.c
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+++ b/hw/virtio/virtio.c
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@@ -3556,6 +3556,17 @@ static void virtio_queue_host_notifier_aio_poll_end(EventNotifier *n)
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void virtio_queue_aio_attach_host_notifier(VirtQueue *vq, AioContext *ctx)
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{
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+ /*
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+ * virtio_queue_aio_detach_host_notifier() can leave notifications disabled.
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+ * Re-enable them. (And if detach has not been used before, notifications
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+ * being enabled is still the default state while a notifier is attached;
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+ * see virtio_queue_host_notifier_aio_poll_end(), which will always leave
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+ * notifications enabled once the polling section is left.)
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+ */
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+ if (!virtio_queue_get_notification(vq)) {
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+ virtio_queue_set_notification(vq, 1);
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+ }
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+
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aio_set_event_notifier(ctx, &vq->host_notifier,
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virtio_queue_host_notifier_read,
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virtio_queue_host_notifier_aio_poll,
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@@ -3563,6 +3574,13 @@ void virtio_queue_aio_attach_host_notifier(VirtQueue *vq, AioContext *ctx)
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aio_set_event_notifier_poll(ctx, &vq->host_notifier,
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virtio_queue_host_notifier_aio_poll_begin,
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virtio_queue_host_notifier_aio_poll_end);
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+
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+ /*
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+ * We will have ignored notifications about new requests from the guest
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+ * while no notifiers were attached, so "kick" the virt queue to process
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+ * those requests now.
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+ */
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+ event_notifier_set(&vq->host_notifier);
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}
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/*
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@@ -3573,14 +3591,38 @@ void virtio_queue_aio_attach_host_notifier(VirtQueue *vq, AioContext *ctx)
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*/
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void virtio_queue_aio_attach_host_notifier_no_poll(VirtQueue *vq, AioContext *ctx)
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{
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+ /* See virtio_queue_aio_attach_host_notifier() */
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+ if (!virtio_queue_get_notification(vq)) {
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+ virtio_queue_set_notification(vq, 1);
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+ }
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+
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aio_set_event_notifier(ctx, &vq->host_notifier,
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virtio_queue_host_notifier_read,
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NULL, NULL);
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+
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+ /*
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+ * See virtio_queue_aio_attach_host_notifier().
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+ * Note that this may be unnecessary for the type of virtqueues this
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+ * function is used for. Still, it will not hurt to have a quick look into
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+ * whether we can/should process any of the virtqueue elements.
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+ */
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+ event_notifier_set(&vq->host_notifier);
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}
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void virtio_queue_aio_detach_host_notifier(VirtQueue *vq, AioContext *ctx)
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{
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aio_set_event_notifier(ctx, &vq->host_notifier, NULL, NULL, NULL);
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+
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+ /*
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+ * aio_set_event_notifier_poll() does not guarantee whether io_poll_end()
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+ * will run after io_poll_begin(), so by removing the notifier, we do not
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+ * know whether virtio_queue_host_notifier_aio_poll_end() has run after a
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+ * previous virtio_queue_host_notifier_aio_poll_begin(), i.e. whether
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+ * notifications are enabled or disabled. It does not really matter anyway;
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+ * we just removed the notifier, so we do not care about notifications until
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+ * we potentially re-attach it. The attach_host_notifier functions will
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+ * ensure that notifications are enabled again when they are needed.
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+ */
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}
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void virtio_queue_host_notifier_read(EventNotifier *n)
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diff --git a/include/block/aio.h b/include/block/aio.h
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index af05512a7d..261c77fd9a 100644
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--- a/include/block/aio.h
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+++ b/include/block/aio.h
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@@ -480,9 +480,14 @@ void aio_set_event_notifier(AioContext *ctx,
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AioPollFn *io_poll,
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EventNotifierHandler *io_poll_ready);
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-/* Set polling begin/end callbacks for an event notifier that has already been
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+/*
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+ * Set polling begin/end callbacks for an event notifier that has already been
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* registered with aio_set_event_notifier. Do nothing if the event notifier is
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* not registered.
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+ *
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+ * Note that if the io_poll_end() callback (or the entire notifier) is removed
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+ * during polling, it will not be called, so an io_poll_begin() is not
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+ * necessarily always followed by an io_poll_end().
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*/
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void aio_set_event_notifier_poll(AioContext *ctx,
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EventNotifier *notifier,
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--
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2.39.3
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