forked from rpms/qemu-kvm
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
66 lines
2.3 KiB
66 lines
2.3 KiB
From df06ce560ddfefde98bef822ec2020382059921f Mon Sep 17 00:00:00 2001
|
|
From: =?UTF-8?q?Eugenio=20P=C3=A9rez?= <eperezma@redhat.com>
|
|
Date: Thu, 21 Jul 2022 15:38:55 +0200
|
|
Subject: [PATCH 10/32] vdpa: Avoid compiler to squash reads to used idx
|
|
MIME-Version: 1.0
|
|
Content-Type: text/plain; charset=UTF-8
|
|
Content-Transfer-Encoding: 8bit
|
|
|
|
RH-Author: Eugenio Pérez <eperezma@redhat.com>
|
|
RH-MergeRequest: 108: Net Control Virtqueue shadow Support
|
|
RH-Commit: [10/27] b28789302d4f64749da26f413763f918161d9b70 (eperezmartin/qemu-kvm)
|
|
RH-Bugzilla: 1939363
|
|
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
|
|
RH-Acked-by: Cindy Lu <lulu@redhat.com>
|
|
RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
|
|
|
|
Bugzilla: https://bugzilla.redhat.com/1939363
|
|
|
|
Upstream Status: git://git.qemu.org/qemu.git
|
|
|
|
commit c381abc37f0aba42ed2e3b41cdace8f8438829e4
|
|
Author: Eugenio Pérez <eperezma@redhat.com>
|
|
Date: Wed Jul 20 08:59:29 2022 +0200
|
|
|
|
vdpa: Avoid compiler to squash reads to used idx
|
|
|
|
In the next patch we will allow busypolling of this value. The compiler
|
|
have a running path where shadow_used_idx, last_used_idx, and vring used
|
|
idx are not modified within the same thread busypolling.
|
|
|
|
This was not an issue before since we always cleared device event
|
|
notifier before checking it, and that could act as memory barrier.
|
|
However, the busypoll needs something similar to kernel READ_ONCE.
|
|
|
|
Let's add it here, sepparated from the polling.
|
|
|
|
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
|
|
Signed-off-by: Jason Wang <jasowang@redhat.com>
|
|
|
|
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
|
|
---
|
|
hw/virtio/vhost-shadow-virtqueue.c | 3 ++-
|
|
1 file changed, 2 insertions(+), 1 deletion(-)
|
|
|
|
diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
|
|
index 3fbda1e3d4..9c46c3a8fa 100644
|
|
--- a/hw/virtio/vhost-shadow-virtqueue.c
|
|
+++ b/hw/virtio/vhost-shadow-virtqueue.c
|
|
@@ -327,11 +327,12 @@ static void vhost_handle_guest_kick_notifier(EventNotifier *n)
|
|
|
|
static bool vhost_svq_more_used(VhostShadowVirtqueue *svq)
|
|
{
|
|
+ uint16_t *used_idx = &svq->vring.used->idx;
|
|
if (svq->last_used_idx != svq->shadow_used_idx) {
|
|
return true;
|
|
}
|
|
|
|
- svq->shadow_used_idx = cpu_to_le16(svq->vring.used->idx);
|
|
+ svq->shadow_used_idx = cpu_to_le16(*(volatile uint16_t *)used_idx);
|
|
|
|
return svq->last_used_idx != svq->shadow_used_idx;
|
|
}
|
|
--
|
|
2.31.1
|
|
|