52 lines
2.0 KiB
Diff
52 lines
2.0 KiB
Diff
From 671f0830d70c1e35deb63cc66db7ce8b713e8967 Mon Sep 17 00:00:00 2001
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From: Stefan Hajnoczi <stefanha@redhat.com>
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Date: Tue, 30 Nov 2021 13:45:10 +0000
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Subject: [PATCH] virtio: signal after wrapping packed used_idx
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Packed Virtqueues wrap used_idx instead of letting it run freely like
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Split Virtqueues do. If the used ring wraps more than once there is no
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way to compare vq->signalled_used and vq->used_idx in
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virtio_packed_should_notify() since they are modulo vq->vring.num.
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This causes the device to stop sending used buffer notifications when
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when virtio_packed_should_notify() is called less than once each time
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around the used ring.
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It is possible to trigger this with virtio-blk's dataplane
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notify_guest_bh() irq coalescing optimization. The call to
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virtio_notify_irqfd() (and virtio_packed_should_notify()) is deferred to
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a BH. If the guest driver is polling it can complete and submit more
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requests before the BH executes, causing the used ring to wrap more than
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once. The result is that the virtio-blk device ceases to raise
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interrupts and I/O hangs.
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Cc: Tiwei Bie <tiwei.bie@intel.com>
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Cc: Jason Wang <jasowang@redhat.com>
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Cc: Michael S. Tsirkin <mst@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Message-Id: <20211130134510.267382-1-stefanha@redhat.com>
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Fixes: 86044b24e865fb9596ed77a4d0f3af8b90a088a1 ("virtio: basic packed virtqueue support")
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Acked-by: Jason Wang <jasowang@redhat.com>
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Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
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Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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Signed-off-by: fangyi <eric.fangyi@huawei.com>
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---
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hw/virtio/virtio.c | 1 +
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1 file changed, 1 insertion(+)
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diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
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index d90cabe868..05409b84d1 100644
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--- a/hw/virtio/virtio.c
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+++ b/hw/virtio/virtio.c
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@@ -885,6 +885,7 @@ static void virtqueue_packed_flush(VirtQueue *vq, unsigned int count)
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if (vq->used_idx >= vq->vring.num) {
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vq->used_idx -= vq->vring.num;
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vq->used_wrap_counter ^= 1;
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+ vq->signalled_used_valid = false;
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}
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}
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--
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2.27.0
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