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Tsirkin" To: Eugenio Perez Martin Cc: Stefano Garzarella , qemu-devel@nongnu.org, jasowang@redhat.com, Peter Maydell , qemu-stable@nongnu.org, Xoykie , Lei Yang Subject: Re: [PATCH] virtio: remove virtio_tswap16s() call in vring_packed_event_read() Message-ID: <20240701063129-mutt-send-email-mst@kernel.org> References: <20240701075208.19634-1-sgarzare@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Jul 01, 2024 at 11:53:34AM +0200, Eugenio Perez Martin wrote: > On Mon, Jul 1, 2024 at 9:52 AM Stefano Garzarella wrote: > > > > Commit d152cdd6f6 ("virtio: use virtio accessor to access packed event") > > switched using of address_space_read_cached() to virito_lduw_phys_cached() > > to access packed descriptor event. > > > > When we used address_space_read_cached(), we needed to call > > virtio_tswap16s() to handle the endianess of the field, but > > virito_lduw_phys_cached() already handles it internally, so we no longer > > need to call virtio_tswap16s() (as the commit had done for `off_wrap`, > > but forgot for `flags`). > > > > Fixes: d152cdd6f6 ("virtio: use virtio accessor to access packed event") > > Cc: jasowang@redhat.com > > Cc: qemu-stable@nongnu.org > > Reported-by: Xoykie > > Link: https://lore.kernel.org/qemu-devel/CAFU8RB_pjr77zMLsM0Unf9xPNxfr_--Tjr49F_eX32ZBc5o2zQ@mail.gmail.com > > Signed-off-by: Stefano Garzarella > > Reviewed-by: Eugenio Pérez > > I think it would be great to test the patches using a big endian host > just in case. > > Thanks! I think we really should move to using sparse tags for endian-ness, like Linux does, and away from swap calls. > > --- > > hw/virtio/virtio.c | 1 - > > 1 file changed, 1 deletion(-) > > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > > index 893a072c9d..2e5e67bdb9 100644 > > --- a/hw/virtio/virtio.c > > +++ b/hw/virtio/virtio.c > > @@ -323,7 +323,6 @@ static void vring_packed_event_read(VirtIODevice *vdev, > > /* Make sure flags is seen before off_wrap */ > > smp_rmb(); > > e->off_wrap = virtio_lduw_phys_cached(vdev, cache, off_off); > > - virtio_tswap16s(vdev, &e->flags); > > } > > > > static void vring_packed_off_wrap_write(VirtIODevice *vdev, > > -- > > 2.45.2 > >