On Thu, Nov 11, 2021 at 02:38:53PM +0800, Jason Wang wrote:
> 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.
Could you clarify where's the memcpy that you see?
Thanks!
> 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-sta...@nongnu.org
> Signed-off-by: Jason Wang <jasow...@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
