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[79.17.248.175]) by smtp.gmail.com with ESMTPSA id p21sm4228345wma.41.2020.11.17.09.38.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Nov 2020 09:38:13 -0800 (PST) Date: Tue, 17 Nov 2020 18:38:11 +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: <20201117173811.lw4nwicoykhnn3tt@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20201117164342.GT131917@stefanha-x1.localdomain> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Thanks, Stefano > >Anyway, the later patch that implements VIRTIO_BLK_T_GET_ID solves this >issue! Thanks. > >Stefan