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From: Jason Wang <jasowang@redhat.com>
To: mst@redhat.com
Cc: eperezma@redhat.com, Jason Wang <jasowang@redhat.com>,
	qemu-devel@nongnu.org, qemu-stable@nongnu.org
Subject: [PATCH 1/2] virtio: use virtio accessor to access packed descriptor flags
Date: Thu, 11 Nov 2021 14:38:53 +0800	[thread overview]
Message-ID: <20211111063854.29060-1-jasowang@redhat.com> (raw)

We used to access packed descriptor flags via
address_space_{write|read}_cached(). When we hit the cache, memcpy()
is used which is not an atomic operation which may lead a wrong value
is read or wrote.

So this patch switches to use virito_{stw|lduw}_phys_cached() to make
sure the aceess is atomic.

Fixes: 86044b24e865f ("virtio: basic packed virtqueue support")
Cc: qemu-stable@nongnu.org
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 hw/virtio/virtio.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index cc69a9b881..939bcbfeb9 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -507,11 +507,9 @@ static void vring_packed_desc_read_flags(VirtIODevice *vdev,
                                          MemoryRegionCache *cache,
                                          int i)
 {
-    address_space_read_cached(cache,
-                              i * sizeof(VRingPackedDesc) +
-                              offsetof(VRingPackedDesc, flags),
-                              flags, sizeof(*flags));
-    virtio_tswap16s(vdev, flags);
+    hwaddr off = i * sizeof(VRingPackedDesc) + offsetof(VRingPackedDesc, flags);
+
+    *flags = virtio_lduw_phys_cached(vdev, cache, off);
 }
 
 static void vring_packed_desc_read(VirtIODevice *vdev,
@@ -564,8 +562,7 @@ static void vring_packed_desc_write_flags(VirtIODevice *vdev,
 {
     hwaddr off = i * sizeof(VRingPackedDesc) + offsetof(VRingPackedDesc, flags);
 
-    virtio_tswap16s(vdev, &desc->flags);
-    address_space_write_cached(cache, off, &desc->flags, sizeof(desc->flags));
+    virtio_stw_phys_cached(vdev, cache, off, desc->flags);
     address_space_cache_invalidate(cache, off, sizeof(desc->flags));
 }
 
-- 
2.25.1



             reply	other threads:[~2021-11-11  6:48 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-11  6:38 Jason Wang [this message]
2021-11-11  6:38 ` [PATCH 2/2] virtio: use virtio accessor to access packed event Jason Wang
2021-11-11  7:51   ` Philippe Mathieu-Daudé
2021-11-12  2:30     ` Jason Wang
2021-11-11  7:51 ` [PATCH 1/2] virtio: use virtio accessor to access packed descriptor flags Philippe Mathieu-Daudé
2021-11-11  8:27 ` Michael S. Tsirkin
2021-11-12  2:23   ` Jason Wang
2021-11-12 10:04     ` Michael S. Tsirkin
2021-11-15  4:20       ` Jason Wang

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