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Tsirkin" Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Received-SPF: pass client-ip=170.10.129.124; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.7, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: eperezma , qemu-devel , qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Nov 11, 2021 at 4:27 PM Michael S. Tsirkin wrote: > > 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! In the address_space_{write|read}_cached it self: static inline MemTxResult =>dress_space_write_cached(MemoryRegionCache *cache, hwaddr addr, const void *buf, hwaddr len) { assert(addr < cache->len && len <= cache->len - addr); if (likely(cache->ptr)) { memcpy(cache->ptr + addr, buf, len); return MEMTX_OK; } else { return address_space_write_cached_slow(cache, addr, buf, len); } } 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-stable@nongnu.org > > Signed-off-by: Jason Wang > > --- > > 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 >