path: root/drivers/scsi/virtio_scsi.c

/*
 * Virtio SCSI HBA driver
 *
 * Copyright IBM Corp. 2010
 * Copyright Red Hat, Inc. 2011
 *
 * Authors:
 *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>
 *  Paolo Bonzini   <pbonzini@redhat.com>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or later.
 * See the COPYING file in the top-level directory.
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/mempool.h>
#include <linux/virtio.h>
#include <linux/virtio_ids.h>
#include <linux/virtio_config.h>
#include <linux/virtio_scsi.h>
#include <linux/cpu.h>
#include <scsi/scsi_host.h>
#include <scsi/scsi_device.h>
#include <scsi/scsi_cmnd.h>

#define VIRTIO_SCSI_MEMPOOL_SZ 64
#define VIRTIO_SCSI_EVENT_LEN 8
#define VIRTIO_SCSI_VQ_BASE 2

/* Command queue element */
struct virtio_scsi_cmd {
	struct scsi_cmnd *sc;
	struct completion *comp;
	union {
		struct virtio_scsi_cmd_req       cmd;
		struct virtio_scsi_ctrl_tmf_req  tmf;
		struct virtio_scsi_ctrl_an_req   an;
	} req;
	union {
		struct virtio_scsi_cmd_resp      cmd;
		struct virtio_scsi_ctrl_tmf_resp tmf;
		struct virtio_scsi_ctrl_an_resp  an;
		struct virtio_scsi_event         evt;
	} resp;
} ____cacheline_aligned_in_smp;

struct virtio_scsi_event_node {
	struct virtio_scsi *vscsi;
	struct virtio_scsi_event event;
	struct work_struct work;
};

struct virtio_scsi_vq {
	/* Protects vq */
	spinlock_t vq_lock;

	struct virtqueue *vq;
};

/*
 * Per-target queue state.
 *
 * This struct holds the data needed by the queue steering policy.  When a
 * target is sent multiple requests, we need to drive them to the same queue so
 * that FIFO processing order is kept.  However, if a target was idle, we can
 * choose a queue arbitrarily.  In this case the queue is chosen according to
 * the current VCPU, so the driver expects the number of request queues to be
 * equal to the number of VCPUs.  This makes it easy and fast to select the
 * queue, and also lets the driver optimize the IRQ affinity for the virtqueues
 * (each virtqueue's affinity is set to the CPU that "owns" the queue).
 *
 * An interesting effect of this policy is that only writes to req_vq need to
 * take the tgt_lock.  Read can be done outside the lock because:
 *
 * - writes of req_vq only occur when atomic_inc_return(&tgt->reqs) returns 1.
 *   In that case, no other CPU is reading req_vq: even if they were in
 *   virtscsi_queuecommand_multi, they would be spinning on tgt_lock.
 *
 * - reads of req_vq only occur when the target is not idle (reqs != 0).
 *   A CPU that enters virtscsi_queuecommand_multi will not modify req_vq.
 *
 * Similarly, decrements of reqs are never concurrent with writes of req_vq.
 * Thus they can happen outside the tgt_lock, provided of course we make reqs
 * an atomic_t.
 */
struct virtio_scsi_target_state {
	/* This spinlock never held at the same time as vq_lock. */
	spinlock_t tgt_lock;

	/* Count of outstanding requests. */
	atomic_t reqs;

	/* Currently active virtqueue for requests sent to this target. */
	struct virtio_scsi_vq *req_vq;
};

/* Driver instance state */
struct virtio_scsi {
	struct virtio_device *vdev;

	/* Get some buffers ready for event vq */
	struct virtio_scsi_event_node event_list[VIRTIO_SCSI_EVENT_LEN];

	u32 num_queues;

	/* If the affinity hint is set for virtqueues */
	bool affinity_hint_set;

	/* CPU hotplug notifier */
	struct notifier_block nb;

	struct virtio_scsi_vq ctrl_vq;
	struct virtio_scsi_vq event_vq;
	struct virtio_scsi_vq req_vqs[];
};

static struct kmem_cache *virtscsi_cmd_cache;
static mempool_t *virtscsi_cmd_pool;

static inline struct Scsi_Host *virtio_scsi_host(struct virtio_device *vdev)
{
	return vdev->priv;
}

static void virtscsi_compute_resid(struct scsi_cmnd *sc, u32 resid)
{
	if (!resid)
		return;

	if (!scsi_bidi_cmnd(sc)) {
		scsi_set_resid(sc, resid);
		return;
	}

	scsi_in(sc)->resid = min(resid, scsi_in(sc)->length);
	scsi_out(sc)->resid = resid - scsi_in(sc)->resid;
}

/**
 * virtscsi_complete_cmd - finish a scsi_cmd and invoke scsi_done
 *
 * Called with vq_lock held.
 */
static void virtscsi_complete_cmd(struct virtio_scsi *vscsi, void *buf)
{
	struct virtio_scsi_cmd *cmd = buf;
	struct scsi_cmnd *sc = cmd->sc;
	struct virtio_scsi_cmd_resp *resp = &cmd->resp.cmd;
	struct virtio_scsi_target_state *tgt =
				scsi_target(sc->device)->hostdata;

	dev_dbg(&sc->device->sdev_gendev,
		"cmd %p response %u status %#02x sense_len %u\n",
		sc, resp->response, resp->status, resp->sense_len);

	sc->result = resp->status;
	virtscsi_compute_resid(sc, resp->resid);
	switch (resp->response) {
	case VIRTIO_SCSI_S_OK:
		set_host_byte(sc, DID_OK);
		break;
	case VIRTIO_SCSI_S_OVERRUN:
		set_host_byte(sc, DID_ERROR);
		break;
	case VIRTIO_SCSI_S_ABORTED:
		set_host_byte(sc, DID_ABORT);
		break;
	case VIRTIO_SCSI_S_BAD_TARGET:
		set_host_byte(sc, DID_BAD_TARGET);
		break;
	case VIRTIO_SCSI_S_RESET:
		set_host_byte(sc, DID_RESET);
		break;
	case VIRTIO_SCSI_S_BUSY:
		set_host_byte(sc, DID_BUS_BUSY);
		break;