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[82.81.31.23]) by smtp.gmail.com with ESMTPSA id y37sm23372137wrd.55.2020.06.07.06.59.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 07 Jun 2020 06:59:02 -0700 (PDT) Date: Sun, 7 Jun 2020 09:59:00 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: linux-kernel@vger.kernel.org, Eugenio =?iso-8859-1?Q?P=E9rez?= , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: Re: [PATCH RFC 01/13] vhost: option to fetch descriptors through an independent struct Message-ID: <20200607095810-mutt-send-email-mst@kernel.org> References: <20200602130543.578420-1-mst@redhat.com> <20200602130543.578420-2-mst@redhat.com> <20200603045825-mutt-send-email-mst@kernel.org> <48e6d644-c4aa-2754-9d06-22133987b3be@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <48e6d644-c4aa-2754-9d06-22133987b3be@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 03, 2020 at 08:04:45PM +0800, Jason Wang wrote: > > On 2020/6/3 下午5:48, Michael S. Tsirkin wrote: > > On Wed, Jun 03, 2020 at 03:13:56PM +0800, Jason Wang wrote: > > > On 2020/6/2 下午9:05, Michael S. Tsirkin wrote: > > > [...] > > > > > > + > > > > +static int fetch_indirect_descs(struct vhost_virtqueue *vq, > > > > + struct vhost_desc *indirect, > > > > + u16 head) > > > > +{ > > > > + struct vring_desc desc; > > > > + unsigned int i = 0, count, found = 0; > > > > + u32 len = indirect->len; > > > > + struct iov_iter from; > > > > + int ret; > > > > + > > > > + /* Sanity check */ > > > > + if (unlikely(len % sizeof desc)) { > > > > + vq_err(vq, "Invalid length in indirect descriptor: " > > > > + "len 0x%llx not multiple of 0x%zx\n", > > > > + (unsigned long long)len, > > > > + sizeof desc); > > > > + return -EINVAL; > > > > + } > > > > + > > > > + ret = translate_desc(vq, indirect->addr, len, vq->indirect, > > > > + UIO_MAXIOV, VHOST_ACCESS_RO); > > > > + if (unlikely(ret < 0)) { > > > > + if (ret != -EAGAIN) > > > > + vq_err(vq, "Translation failure %d in indirect.\n", ret); > > > > + return ret; > > > > + } > > > > + iov_iter_init(&from, READ, vq->indirect, ret, len); > > > > + > > > > + /* We will use the result as an address to read from, so most > > > > + * architectures only need a compiler barrier here. */ > > > > + read_barrier_depends(); > > > > + > > > > + count = len / sizeof desc; > > > > + /* Buffers are chained via a 16 bit next field, so > > > > + * we can have at most 2^16 of these. */ > > > > + if (unlikely(count > USHRT_MAX + 1)) { > > > > + vq_err(vq, "Indirect buffer length too big: %d\n", > > > > + indirect->len); > > > > + return -E2BIG; > > > > + } > > > > + if (unlikely(vq->ndescs + count > vq->max_descs)) { > > > > + vq_err(vq, "Too many indirect + direct descs: %d + %d\n", > > > > + vq->ndescs, indirect->len); > > > > + return -E2BIG; > > > > + } > > > > + > > > > + do { > > > > + if (unlikely(++found > count)) { > > > > + vq_err(vq, "Loop detected: last one at %u " > > > > + "indirect size %u\n", > > > > + i, count); > > > > + return -EINVAL; > > > > + } > > > > + if (unlikely(!copy_from_iter_full(&desc, sizeof(desc), &from))) { > > > > + vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n", > > > > + i, (size_t)indirect->addr + i * sizeof desc); > > > > + return -EINVAL; > > > > + } > > > > + if (unlikely(desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT))) { > > > > + vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n", > > > > + i, (size_t)indirect->addr + i * sizeof desc); > > > > + return -EINVAL; > > > > + } > > > > + > > > > + push_split_desc(vq, &desc, head); > > > > > > The error is ignored. > > See above: > > > > if (unlikely(vq->ndescs + count > vq->max_descs)) > > > > So it can't fail here, we never fetch unless there's space. > > > > I guess we can add a WARN_ON here. > > > Yes. > > > > > > > > + } while ((i = next_desc(vq, &desc)) != -1); > > > > + return 0; > > > > +} > > > > + > > > > +static int fetch_descs(struct vhost_virtqueue *vq) > > > > +{ > > > > + unsigned int i, head, found = 0; > > > > + struct vhost_desc *last; > > > > + struct vring_desc desc; > > > > + __virtio16 avail_idx; > > > > + __virtio16 ring_head; > > > > + u16 last_avail_idx; > > > > + int ret; > > > > + > > > > + /* Check it isn't doing very strange things with descriptor numbers. */ > > > > + last_avail_idx = vq->last_avail_idx; > > > > + > > > > + if (vq->avail_idx == vq->last_avail_idx) { > > > > + if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) { > > > > + vq_err(vq, "Failed to access avail idx at %p\n", > > > > + &vq->avail->idx); > > > > + return -EFAULT; > > > > + } > > > > + vq->avail_idx = vhost16_to_cpu(vq, avail_idx); > > > > + > > > > + if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) { > > > > + vq_err(vq, "Guest moved used index from %u to %u", > > > > + last_avail_idx, vq->avail_idx); > > > > + return -EFAULT; > > > > + } > > > > + > > > > + /* If there's nothing new since last we looked, return > > > > + * invalid. > > > > + */ > > > > + if (vq->avail_idx == last_avail_idx) > > > > + return vq->num; > > > > + > > > > + /* Only get avail ring entries after they have been > > > > + * exposed by guest. > > > > + */ > > > > + smp_rmb(); > > > > + } > > > > + > > > > + /* Grab the next descriptor number they're advertising */ > > > > + if (unlikely(vhost_get_avail_head(vq, &ring_head, last_avail_idx))) { > > > > + vq_err(vq, "Failed to read head: idx %d address %p\n", > > > > + last_avail_idx, > > > > + &vq->avail->ring[last_avail_idx % vq->num]); > > > > + return -EFAULT; > > > > + } > > > > + > > > > + head = vhost16_to_cpu(vq, ring_head); > > > > + > > > > + /* If their number is silly, that's an error. */ > > > > + if (unlikely(head >= vq->num)) { > > > > + vq_err(vq, "Guest says index %u > %u is available", > > > > + head, vq->num); > > > > + return -EINVAL; > > > > + } > > > > + > > > > + i = head; > > > > + do { > > > > + if (unlikely(i >= vq->num)) { > > > > + vq_err(vq, "Desc index is %u > %u, head = %u", > > > > + i, vq->num, head); > > > > + return -EINVAL; > > > > + } > > > > + if (unlikely(++found > vq->num)) { > > > > + vq_err(vq, "Loop detected: last one at %u " > > > > + "vq size %u head %u\n", > > > > + i, vq->num, head); > > > > + return -EINVAL; > > > > + } > > > > + ret = vhost_get_desc(vq, &desc, i); > > > > + if (unlikely(ret)) { > > > > + vq_err(vq, "Failed to get descriptor: idx %d addr %p\n", > > > > + i, vq->desc + i); > > > > + return -EFAULT; > > > > + } > > > > + ret = push_split_desc(vq, &desc, head); > > > > + if (unlikely(ret)) { > > > > + vq_err(vq, "Failed to save descriptor: idx %d\n", i); > > > > + return -EINVAL; > > > > + } > > > > + } while ((i = next_desc(vq, &desc)) != -1); > > > > + > > > > + last = peek_split_desc(vq); > > > > + if (unlikely(last->flags & VRING_DESC_F_INDIRECT)) { > > > > + pop_split_desc(vq); > > > > + ret = fetch_indirect_descs(vq, last, head); > > > > > > Note that this means we don't supported chained indirect descriptors which > > > complies the spec but we support this in vhost_get_vq_desc(). > > Well the spec says: > > A driver MUST NOT set both VIRTQ_DESC_F_INDIRECT and VIRTQ_DESC_F_NEXT in flags. > > > > Did I miss anything? > > > > No, but I meant current vhost_get_vq_desc() supports chained indirect > descriptor. Not sure if there's an application that depends on this > silently. > > Thanks > I don't think we need to worry about that unless this actually surfaces. -- MST