[PATCH-v3 5/9] vhost/scsi: Add ANY_LAYOUT vhost_virtqueue callback

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From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>

This patch adds ANY_LAYOUT support with a new vqs[].vq.handle_kick()
callback in vhost_scsi_handle_vqal().

It calculates data_direction + exp_data_len for the new tcm_vhost_cmd
descriptor by walking both outgoing + incoming iovecs using iov_iter,
assuming the layout of outgoing request header + T10_PI + Data payload
comes first.

It also uses copy_from_iter() to copy leading virtio-scsi request header
that may or may not include SCSI CDB, that returns a re-calculated iovec
to start of T10_PI or Data SGL memory.

v2 changes:
  - Fix up vhost_scsi_handle_vqal comments
  - Minor vhost_scsi_handle_vqal simplifications
  - Add missing minimum virtio-scsi response buffer size check
  - Fix pi_bytes* error message typo
  - Convert to use vhost_skip_iovec_bytes() common code
  - Add max_niov sanity checks vs. out + in offset into vq

v3 changes:
  - Convert to copy_from_iter usage
  - Update vhost_scsi_handle_vqal comments for iov_iter usage
  - Convert prot_bytes offset to use iov_iter_advance
  - Drop max_niov usage in vhost_scsi_handle_vqal
  - Drop vhost_skip_iovec_bytes in favour of iov_iter

Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
---
 drivers/vhost/scsi.c | 260 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 260 insertions(+)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 7dfff15..e1fe003 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1062,6 +1062,266 @@ vhost_scsi_send_bad_target(struct vhost_scsi *vs,
 }
 
 static void
+vhost_scsi_handle_vqal(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
+{
+	struct tcm_vhost_tpg **vs_tpg, *tpg;
+	struct virtio_scsi_cmd_req v_req;
+	struct virtio_scsi_cmd_req_pi v_req_pi;
+	struct tcm_vhost_cmd *cmd;
+	struct iov_iter out_iter, in_iter, prot_iter, data_iter;
+	u64 tag;
+	u32 exp_data_len, data_direction;
+	unsigned out, in, i;
+	int head, ret, prot_bytes;
+	size_t req_size, rsp_size = sizeof(struct virtio_scsi_cmd_resp);
+	size_t out_size, in_size;
+	u16 lun;
+	u8 *target, *lunp, task_attr;
+	bool t10_pi = vhost_has_feature(vq, VIRTIO_SCSI_F_T10_PI);
+	void *req, *cdb;
+
+	mutex_lock(&vq->mutex);
+	/*
+	 * We can handle the vq only after the endpoint is setup by calling the
+	 * VHOST_SCSI_SET_ENDPOINT ioctl.
+	 */
+	vs_tpg = vq->private_data;
+	if (!vs_tpg)
+		goto out;
+
+	vhost_disable_notify(&vs->dev, vq);
+
+	for (;;) {
+		head = vhost_get_vq_desc(vq, vq->iov,
+					 ARRAY_SIZE(vq->iov), &out, &in,
+					 NULL, NULL);
+		pr_debug("vhost_get_vq_desc: head: %d, out: %u in: %u\n",
+			 head, out, in);
+		/* On error, stop handling until the next kick. */
+		if (unlikely(head < 0))
+			break;
+		/* Nothing new?  Wait for eventfd to tell us they refilled. */
+		if (head == vq->num) {
+			if (unlikely(vhost_enable_notify(&vs->dev, vq))) {
+				vhost_disable_notify(&vs->dev, vq);
+				continue;
+			}
+			break;
+		}
+		/*
+		 * Check for a sane response buffer so we can report early
+		 * errors back to the guest.
+		 */
+		if (unlikely(vq->iov[out].iov_len < rsp_size)) {
+			vq_err(vq, "Expecting at least virtio_scsi_cmd_resp"
+				" size, got %zu bytes\n", vq->iov[out].iov_len);
+			break;
+		}
+		/*
+		 * Setup pointers and values based upon different virtio-scsi
+		 * request header if T10_PI is enabled in KVM guest.
+		 */
+		if (t10_pi) {
+			req = &v_req_pi;
+			req_size = sizeof(v_req_pi);
+			lunp = &v_req_pi.lun[0];
+			target = &v_req_pi.lun[1];
+		} else {
+			req = &v_req;
+			req_size = sizeof(v_req);
+			lunp = &v_req.lun[0];
+			target = &v_req.lun[1];
+		}
+		/*
+		 * Determine data_direction for ANY_LAYOUT by calculating the
+		 * total outgoing iovec sizes / incoming iovec sizes vs.
+		 * virtio-scsi request / response headers respectively.
+		 *
+		 * FIXME: Not correct for BIDI operation
+		 */
+		out_size = in_size = 0;
+		for (i = 0; i < out; i++)
+			out_size += vq->iov[i].iov_len;
+		for (i = out; i < out + in; i++)
+			in_size += vq->iov[i].iov_len;
+		/*
+		 * Any associated T10_PI bytes for the outgoing / incoming
+		 * payloads are included in calculation of exp_data_len here.
+		 */
+		if (out_size > req_size) {
+			data_direction = DMA_TO_DEVICE;
+			exp_data_len = out_size - req_size;
+		} else if (in_size > rsp_size) {
+			data_direction = DMA_FROM_DEVICE;
+			exp_data_len = in_size - rsp_size;
+		} else {
+			data_direction = DMA_NONE;
+			exp_data_len = 0;
+		}
+		/*
+		 * Copy over the virtio-scsi request header, which when
+		 * ANY_LAYOUT is enabled may span multiple iovecs, or a
+		 * single iovec may contain both the header + outgoing
+		 * WRITE payloads.
+		 *
+		 * copy_from_iter() is modifying the iovecs as copies over
+		 * req_size bytes into req, so the returned out_iter.iov[0]
+		 * will contain the correct start + offset of the outgoing
+		 * WRITE payload, if DMA_TO_DEVICE is set.
+		 */
+		iov_iter_init(&out_iter, READ, &vq->iov[0], out,
+			     (data_direction == DMA_TO_DEVICE) ?
+			      req_size + exp_data_len : req_size);
+
+		ret = copy_from_iter(req, req_size, &out_iter);
+		if (unlikely(ret != req_size)) {
+			vq_err(vq, "Faulted on copy_from_iter\n");
+			vhost_scsi_send_bad_target(vs, vq, head, out);
+			continue;
+		}
+		/* virtio-scsi spec requires byte 0 of the lun to be 1 */
+		if (unlikely(*lunp != 1)) {
+			vq_err(vq, "Illegal virtio-scsi lun: %u\n", *lunp);
+			vhost_scsi_send_bad_target(vs, vq, head, out);
+			continue;
+		}
+
+		tpg = ACCESS_ONCE(vs_tpg[*target]);
+		if (unlikely(!tpg)) {
+			/* Target does not exist, fail the request */
+			vhost_scsi_send_bad_target(vs, vq, head, out);
+			continue;
+		}
+		/*
+		 * Determine start of T10_PI or data payload iovec in ANY_LAYOUT
+		 * mode based upon data_direction.
+		 *
+		 * For DMA_TO_DEVICE, this is iov_out from copy_from_iter()
+		 * with the already recalculated iov_base + iov_len.
+		 *
+		 * For DMA_FROM_DEVICE, the iovec will be just past the end
+		 * of the virtio-scsi response header in either the same
+		 * or immediately following iovec.
+		 */
+		prot_bytes = 0;
+
+		if (data_direction == DMA_TO_DEVICE) {
+			data_iter = out_iter;
+		} else if (data_direction == DMA_FROM_DEVICE) {
+			iov_iter_init(&in_iter, WRITE, &vq->iov[out], in,
+				      rsp_size + exp_data_len);
+			iov_iter_advance(&in_iter, rsp_size);
+			data_iter = in_iter;
+		}
+		/*
+		 * If T10_PI header + payload is present, setup prot_iter values
+		 * and recalculate data_iter for vhost_scsi_mapal() mapping to
+		 * host scatterlists via get_user_pages_fast().
+		 */
+		if (t10_pi) {
+			if (v_req_pi.pi_bytesout) {
+				if (data_direction != DMA_TO_DEVICE) {
+					vq_err(vq, "Received non zero pi_bytesout,"
+						" but wrong data_direction\n");
+					vhost_scsi_send_bad_target(vs, vq, head, out);
+					continue;
+				}
+				prot_bytes = vhost32_to_cpu(vq, v_req_pi.pi_bytesout);
+			} else if (v_req_pi.pi_bytesin) {
+				if (data_direction != DMA_FROM_DEVICE) {
+					vq_err(vq, "Received non zero pi_bytesin,"
+						" but wrong data_direction\n");
+					vhost_scsi_send_bad_target(vs, vq, head, out);
+					continue;
+				}
+				prot_bytes = vhost32_to_cpu(vq, v_req_pi.pi_bytesin);
+			}
+			/*
+			 * Set prot_iter to data_iter, and advance past any
+			 * preceeding prot_bytes that may be present.
+			 *
+			 * Also fix up the exp_data_len to reflect only the
+			 * actual data payload length.
+			 */
+			if (prot_bytes) {
+				exp_data_len -= prot_bytes;
+				prot_iter = data_iter;
+				iov_iter_advance(&data_iter, prot_bytes);
+			}
+			tag = vhost64_to_cpu(vq, v_req_pi.tag);
+			task_attr = v_req_pi.task_attr;
+			cdb = &v_req_pi.cdb[0];
+			lun = ((v_req_pi.lun[2] << 8) | v_req_pi.lun[3]) & 0x3FFF;
+		} else {
+			tag = vhost64_to_cpu(vq, v_req.tag);
+			task_attr = v_req.task_attr;
+			cdb = &v_req.cdb[0];
+			lun = ((v_req.lun[2] << 8) | v_req.lun[3]) & 0x3FFF;
+		}
+		/*
+		 * Check that the recieved CDB size does not exceeded our
+		 * hardcoded max for vhost-scsi, then get a pre-allocated
+		 * cmd descriptor for the new virtio-scsi tag.
+		 *
+		 * TODO what if cdb was too small for varlen cdb header?
+		 */
+		if (unlikely(scsi_command_size(cdb) > TCM_VHOST_MAX_CDB_SIZE)) {
+			vq_err(vq, "Received SCSI CDB with command_size: %d that"
+				" exceeds SCSI_MAX_VARLEN_CDB_SIZE: %d\n",
+				scsi_command_size(cdb), TCM_VHOST_MAX_CDB_SIZE);
+			vhost_scsi_send_bad_target(vs, vq, head, out);
+			continue;
+		}
+		cmd = vhost_scsi_get_tag(vq, tpg, cdb, tag, lun, task_attr,
+					 exp_data_len + prot_bytes,
+					 data_direction);
+		if (IS_ERR(cmd)) {
+			vq_err(vq, "vhost_scsi_get_tag failed %ld\n",
+			       PTR_ERR(cmd));
+			vhost_scsi_send_bad_target(vs, vq, head, out);
+			continue;
+		}
+		cmd->tvc_vhost = vs;
+		cmd->tvc_vq = vq;
+		cmd->tvc_resp_iov = &vq->iov[out];
+		cmd->tvc_in_iovs = in;
+
+		pr_debug("vhost_scsi got command opcode: %#02x, lun: %d\n",
+			 cmd->tvc_cdb[0], cmd->tvc_lun);
+		pr_debug("cmd: %p exp_data_len: %d, prot_bytes: %d data_direction:"
+			 " %d\n", cmd, exp_data_len, prot_bytes, data_direction);
+
+		if (data_direction != DMA_NONE) {
+			ret = vhost_scsi_mapal(cmd,
+					       prot_bytes, &prot_iter,
+					       exp_data_len, &data_iter);
+			if (unlikely(ret)) {
+				vq_err(vq, "Failed to map iov to sgl\n");
+				tcm_vhost_release_cmd(&cmd->tvc_se_cmd);
+				vhost_scsi_send_bad_target(vs, vq, head, out);
+				continue;
+			}
+		}
+		/*
+		 * Save the descriptor from vhost_get_vq_desc() to be used to
+		 * complete the virtio-scsi request in TCM callback context via
+		 * vhost_scsi_queue_data_in() and vhost_scsi_queue_status()
+		 */
+		cmd->tvc_vq_desc = head;
+		/*
+		 * Dispatch cmd descriptor for cmwq execution in process
+		 * context provided by vhost_scsi_workqueue.  This also ensures
+		 * cmd is executed on the same kworker CPU as this vhost
+		 * thread to gain positive L2 cache locality effects.
+		 */
+		INIT_WORK(&cmd->work, tcm_vhost_submission_work);
+		queue_work(tcm_vhost_workqueue, &cmd->work);
+	}
+out:
+	mutex_unlock(&vq->mutex);
+}
+
+static void
 vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 {
 	struct tcm_vhost_tpg **vs_tpg;
-- 
1.9.1

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