47 lines
1.7 KiB
Diff
47 lines
1.7 KiB
Diff
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From 853f14a29c9a31ca132647770f7d6886103b2b77 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Eugenio=20P=C3=A9rez?= <eperezma@redhat.com>
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Date: Wed, 20 Jul 2022 08:59:29 +0200
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Subject: [PATCH] vdpa: Avoid compiler to squash reads to used idx
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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In the next patch we will allow busypolling of this value. The compiler
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have a running path where shadow_used_idx, last_used_idx, and vring used
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idx are not modified within the same thread busypolling.
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This was not an issue before since we always cleared device event
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notifier before checking it, and that could act as memory barrier.
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However, the busypoll needs something similar to kernel READ_ONCE.
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Let's add it here, sepparated from the polling.
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Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
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Signed-off-by: Jason Wang <jasowang@redhat.com>
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Signed-off-by: fangyi <eric.fangyi@huawei.com>
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---
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hw/virtio/vhost-shadow-virtqueue.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
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index da1e1ce3c7..acf50a9a0b 100644
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--- a/hw/virtio/vhost-shadow-virtqueue.c
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+++ b/hw/virtio/vhost-shadow-virtqueue.c
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@@ -326,11 +326,12 @@ static void vhost_handle_guest_kick_notifier(EventNotifier *n)
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static bool vhost_svq_more_used(VhostShadowVirtqueue *svq)
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{
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+ uint16_t *used_idx = &svq->vring.used->idx;
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if (svq->last_used_idx != svq->shadow_used_idx) {
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return true;
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}
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- svq->shadow_used_idx = cpu_to_le16(svq->vring.used->idx);
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+ svq->shadow_used_idx = cpu_to_le16(*(volatile uint16_t *)used_idx);
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return svq->last_used_idx != svq->shadow_used_idx;
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}
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--
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2.27.0
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