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[79.17.248.175]) by smtp.gmail.com with ESMTPSA id y16sm31384125wrt.25.2020.11.18.03.39.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Nov 2020 03:39:33 -0800 (PST) Date: Wed, 18 Nov 2020 12:39:30 +0100 From: Stefano Garzarella To: Stefan Hajnoczi Cc: virtualization@lists.linux-foundation.org, Laurent Vivier , linux-kernel@vger.kernel.org, Eli Cohen , Jason Wang , "Michael S. Tsirkin" , Max Gurtovoy Subject: Re: [PATCH RFC 04/12] vdpa: add vdpa simulator for block device Message-ID: <20201118113930.p7uigootcb42wqix@steredhat> References: <20201113134712.69744-1-sgarzare@redhat.com> <20201113134712.69744-5-sgarzare@redhat.com> <20201117111121.GD131917@stefanha-x1.localdomain> <20201117141620.ytium7r6xpxi4and@steredhat> <20201117164342.GT131917@stefanha-x1.localdomain> <20201117173811.lw4nwicoykhnn3tt@steredhat> <20201118112355.GE182763@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20201118112355.GE182763@stefanha-x1.localdomain> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 18, 2020 at 11:23:55AM +0000, Stefan Hajnoczi wrote: >On Tue, Nov 17, 2020 at 06:38:11PM +0100, Stefano Garzarella wrote: >> On Tue, Nov 17, 2020 at 04:43:42PM +0000, Stefan Hajnoczi wrote: >> > On Tue, Nov 17, 2020 at 03:16:20PM +0100, Stefano Garzarella wrote: >> > > On Tue, Nov 17, 2020 at 11:11:21AM +0000, Stefan Hajnoczi wrote: >> > > > On Fri, Nov 13, 2020 at 02:47:04PM +0100, Stefano Garzarella wrote: >> > > > > +static void vdpasim_blk_work(struct work_struct *work) >> > > > > +{ >> > > > > + struct vdpasim *vdpasim = container_of(work, struct vdpasim, work); >> > > > > + u8 status = VIRTIO_BLK_S_OK; >> > > > > + int i; >> > > > > + >> > > > > + spin_lock(&vdpasim->lock); >> > > > > + >> > > > > + if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK)) >> > > > > + goto out; >> > > > > + >> > > > > + for (i = 0; i < VDPASIM_BLK_VQ_NUM; i++) { >> > > > > + struct vdpasim_virtqueue *vq = &vdpasim->vqs[i]; >> > > > > + >> > > > > + if (!vq->ready) >> > > > > + continue; >> > > > > + >> > > > > + while (vringh_getdesc_iotlb(&vq->vring, &vq->iov, &vq->iov, >> > > > > + &vq->head, GFP_ATOMIC) > 0) { >> > > > > + >> > > > > + int write; >> > > > > + >> > > > > + vq->iov.i = vq->iov.used - 1; >> > > > > + write = vringh_iov_push_iotlb(&vq->vring, &vq->iov, &status, 1); >> > > > > + if (write <= 0) >> > > > > + break; >> > > > >> > > > We're lucky the guest driver doesn't crash after VIRTIO_BLK_T_GET_ID? :) >> > > >> > > The crash could happen if the simulator doesn't put the string terminator, >> > > but in virtio_blk.c, the serial_show() initialize the buffer putting the >> > > string terminator in the VIRTIO_BLK_ID_BYTES element: >> > > >> > > buf[VIRTIO_BLK_ID_BYTES] = '\0'; >> > > err = virtblk_get_id(disk, buf); >> > > >> > > This should prevent the issue, right? >> > > >> > > However in the last patch of this series I implemented VIRTIO_BLK_T_GET_ID >> > > support :-) >> > >> > Windows, BSD, macOS, etc guest drivers aren't necessarily going to >> > terminate or initialize the serial string buffer. >> >> Unfortunately I discovered that VIRTIO_BLK_T_GET_ID is not in the VIRTIO >> specs, so, just for curiosity, I checked the QEMU code and I found this: >> >> case VIRTIO_BLK_T_GET_ID: >> { >> /* >> * NB: per existing s/n string convention the string is >> * terminated by '\0' only when shorter than buffer. >> */ >> const char *serial = s->conf.serial ? s->conf.serial : ""; >> size_t size = MIN(strlen(serial) + 1, >> MIN(iov_size(in_iov, in_num), >> VIRTIO_BLK_ID_BYTES)); >> iov_from_buf(in_iov, in_num, 0, serial, size); >> virtio_blk_req_complete(req, VIRTIO_BLK_S_OK); >> virtio_blk_free_request(req); >> break; >> } >> >> It seems that the device emulation in QEMU expects that the driver >> terminates the serial string buffer. >> >> Do you know why VIRTIO_BLK_T_GET_ID is not in the specs? >> Should we add it? > >It's about to be merged into the VIRTIO spec: >https://github.com/oasis-tcs/virtio-spec/issues/63 > Great! Thanks for the link! Stefano