virtio_pci: optional MSI-X support

This implements optional MSI-X support in virtio_pci.
MSI-X is used whenever the host supports at least 2 MSI-X
vectors: 1 for configuration changes and 1 for virtqueues.
Per-virtqueue vectors are allocated if enough vectors
available.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (+ whitespace, style)

1 files changed, 209 insertions, 19 deletions

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 951e673e50a4..193c8f0e5cc5 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -42,6 +42,26 @@ struct virtio_pci_device
         /* a list of queues so we can dispatch IRQs */
         spinlock_t lock;
         struct list_head virtqueues;
+
+        /* MSI-X support */
+        int msix_enabled;
+        int intx_enabled;
+        struct msix_entry *msix_entries;
+        /* Name strings for interrupts. This size should be enough,
+         * and I'm too lazy to allocate each name separately. */
+        char (*msix_names)[256];
+        /* Number of available vectors */
+        unsigned msix_vectors;
+        /* Vectors allocated */
+        unsigned msix_used_vectors;
+};
+
+/* Constants for MSI-X */
+/* Use first vector for configuration changes, second and the rest for
+ * virtqueues Thus, we need at least 2 vectors for MSI. */
+enum {
+        VP_MSIX_CONFIG_VECTOR = 0,
+        VP_MSIX_VQ_VECTOR = 1,
 };
 
 struct virtio_pci_vq_info
@@ -60,6 +80,9 @@ struct virtio_pci_vq_info
 
         /* the list node for the virtqueues list */
         struct list_head node;
+
+        /* MSI-X vector (or none) */
+        unsigned vector;
 };
 
 /* Qumranet donated their vendor ID for devices 0x1000 thru 0x10FF. */
@@ -109,7 +132,8 @@ static void vp_get(struct virtio_device *vdev, unsigned offset,
                    void *buf, unsigned len)
 {
         struct virtio_pci_device *vp_dev = to_vp_device(vdev);
-        void __iomem *ioaddr = vp_dev->ioaddr + VIRTIO_PCI_CONFIG + offset;
+        void __iomem *ioaddr = vp_dev->ioaddr +
+                                VIRTIO_PCI_CONFIG(vp_dev) + offset;
         u8 *ptr = buf;
         int i;
 
@@ -123,7 +147,8 @@ static void vp_set(struct virtio_device *vdev, unsigned offset,
                    const void *buf, unsigned len)
 {
         struct virtio_pci_device *vp_dev = to_vp_device(vdev);
-        void __iomem *ioaddr = vp_dev->ioaddr + VIRTIO_PCI_CONFIG + offset;
+        void __iomem *ioaddr = vp_dev->ioaddr +
+                                VIRTIO_PCI_CONFIG(vp_dev) + offset;
         const u8 *ptr = buf;
         int i;
 
@@ -221,7 +246,122 @@ static irqreturn_t vp_interrupt(int irq, void *opaque)
         return vp_vring_interrupt(irq, opaque);
 }
 
-/* the config->find_vq() implementation */
+static void vp_free_vectors(struct virtio_device *vdev)
+{
+        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
+        int i;
+
+        if (vp_dev->intx_enabled) {
+                free_irq(vp_dev->pci_dev->irq, vp_dev);
+                vp_dev->intx_enabled = 0;
+        }
+
+        for (i = 0; i < vp_dev->msix_used_vectors; ++i)
+                free_irq(vp_dev->msix_entries[i].vector, vp_dev);
+        vp_dev->msix_used_vectors = 0;
+
+        if (vp_dev->msix_enabled) {
+                /* Disable the vector used for configuration */
+                iowrite16(VIRTIO_MSI_NO_VECTOR,
+                          vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
+                /* Flush the write out to device */
+                ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
+
+                vp_dev->msix_enabled = 0;
+                pci_disable_msix(vp_dev->pci_dev);
+        }
+}
+
+static int vp_enable_msix(struct pci_dev *dev, struct msix_entry *entries,
+                          int *options, int noptions)
+{
+        int i;
+        for (i = 0; i < noptions; ++i)
+                if (!pci_enable_msix(dev, entries, options[i]))
+                        return options[i];
+        return -EBUSY;
+}
+
+static int vp_request_vectors(struct virtio_device *vdev, unsigned max_vqs)
+{
+        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
+        const char *name = dev_name(&vp_dev->vdev.dev);
+        unsigned i, v;
+        int err = -ENOMEM;
+        /* We want at most one vector per queue and one for config changes.
+         * Fallback to separate vectors for config and a shared for queues.
+         * Finally fall back to regular interrupts. */
+        int options[] = { max_vqs + 1, 2 };
+        int nvectors = max(options[0], options[1]);
+
+        vp_dev->msix_entries = kmalloc(nvectors * sizeof *vp_dev->msix_entries,
+                                       GFP_KERNEL);
+        if (!vp_dev->msix_entries)
+                goto error_entries;
+        vp_dev->msix_names = kmalloc(nvectors * sizeof *vp_dev->msix_names,
+                                     GFP_KERNEL);
+        if (!vp_dev->msix_names)
+                goto error_names;
+
+        for (i = 0; i < nvectors; ++i)
+                vp_dev->msix_entries[i].entry = i;
+
+        err = vp_enable_msix(vp_dev->pci_dev, vp_dev->msix_entries,
+                             options, ARRAY_SIZE(options));
+        if (err < 0) {
+                /* Can't allocate enough MSI-X vectors, use regular interrupt */
+                vp_dev->msix_vectors = 0;
+                err = request_irq(vp_dev->pci_dev->irq, vp_interrupt,
+                                  IRQF_SHARED, name, vp_dev);
+                if (err)
+                        goto error_irq;
+                vp_dev->intx_enabled = 1;
+        } else {
+                vp_dev->msix_vectors = err;
+                vp_dev->msix_enabled = 1;
+
+                /* Set the vector used for configuration */
+                v = vp_dev->msix_used_vectors;
+                snprintf(vp_dev->msix_names[v], sizeof *vp_dev->msix_names,
+                         "%s-config", name);
+                err = request_irq(vp_dev->msix_entries[v].vector,
+                                  vp_config_changed, 0, vp_dev->msix_names[v],
+                                  vp_dev);
+                if (err)
+                        goto error_irq;
+                ++vp_dev->msix_used_vectors;
+
+                iowrite16(v, vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
+                /* Verify we had enough resources to assign the vector */
+                v = ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
+                if (v == VIRTIO_MSI_NO_VECTOR) {
+                        err = -EBUSY;
+                        goto error_irq;
+                }
+        }
+
+        if (vp_dev->msix_vectors && vp_dev->msix_vectors != max_vqs + 1) {
+                /* Shared vector for all VQs */
+                v = vp_dev->msix_used_vectors;
+                snprintf(vp_dev->msix_names[v], sizeof *vp_dev->msix_names,
+                         "%s-virtqueues", name);
+                err = request_irq(vp_dev->msix_entries[v].vector,
+                                  vp_vring_interrupt, 0, vp_dev->msix_names[v],
+                                  vp_dev);
+                if (err)
+                        goto error_irq;
+                ++vp_dev->msix_used_vectors;
+        }
+        return 0;
+error_irq:
+        vp_free_vectors(vdev);
+        kfree(vp_dev->msix_names);
+error_names:
+        kfree(vp_dev->msix_entries);
+error_entries:
+        return err;
+}
+
 static struct virtqueue *vp_find_vq(struct virtio_device *vdev, unsigned index,
                                     void (*callback)(struct virtqueue *vq),
                                     const char *name)
@@ -230,7 +370,7 @@ static struct virtqueue *vp_find_vq(struct virtio_device *vdev, unsigned index,
         struct virtio_pci_vq_info *info;
         struct virtqueue *vq;
         unsigned long flags, size;
-        u16 num;
+        u16 num, vector;
         int err;
 
         /* Select the queue we're interested in */
@@ -249,6 +389,7 @@ static struct virtqueue *vp_find_vq(struct virtio_device *vdev, unsigned index,
 
         info->queue_index = index;
         info->num = num;
+        info->vector = VIRTIO_MSI_NO_VECTOR;
 
         size = PAGE_ALIGN(vring_size(num, VIRTIO_PCI_VRING_ALIGN));
         info->queue = alloc_pages_exact(size, GFP_KERNEL|__GFP_ZERO);
@@ -272,12 +413,43 @@ static struct virtqueue *vp_find_vq(struct virtio_device *vdev, unsigned index,
         vq->priv = info;
         info->vq = vq;
 
+        /* allocate per-vq vector if available and necessary */
+        if (callback && vp_dev->msix_used_vectors < vp_dev->msix_vectors) {
+                vector = vp_dev->msix_used_vectors;
+                snprintf(vp_dev->msix_names[vector], sizeof *vp_dev->msix_names,
+                         "%s-%s", dev_name(&vp_dev->vdev.dev), name);
+                err = request_irq(vp_dev->msix_entries[vector].vector,
+                                  vring_interrupt, 0,
+                                  vp_dev->msix_names[vector], vq);
+                if (err)
+                        goto out_request_irq;
+                info->vector = vector;
+                ++vp_dev->msix_used_vectors;
+        } else
+                vector = VP_MSIX_VQ_VECTOR;
+
+         if (callback && vp_dev->msix_enabled) {
+                iowrite16(vector, vp_dev->ioaddr + VIRTIO_MSI_QUEUE_VECTOR);
+                vector = ioread16(vp_dev->ioaddr + VIRTIO_MSI_QUEUE_VECTOR);
+                if (vector == VIRTIO_MSI_NO_VECTOR) {
+                        err = -EBUSY;
+                        goto out_assign;
+                }
+        }
+
         spin_lock_irqsave(&vp_dev->lock, flags);
         list_add(&info->node, &vp_dev->virtqueues);
         spin_unlock_irqrestore(&vp_dev->lock, flags);
 
         return vq;
 
+out_assign:
+        if (info->vector != VIRTIO_MSI_NO_VECTOR) {
+                free_irq(vp_dev->msix_entries[info->vector].vector, vq);
+                --vp_dev->msix_used_vectors;
+        }
+out_request_irq:
+        vring_del_virtqueue(vq);
 out_activate_queue:
         iowrite32(0, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);
         free_pages_exact(info->queue, size);
@@ -286,17 +458,27 @@ out_info:
         return ERR_PTR(err);
 }
 
-/* the config->del_vq() implementation */
 static void vp_del_vq(struct virtqueue *vq)
 {
         struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev);
         struct virtio_pci_vq_info *info = vq->priv;
         unsigned long size;
 
+        iowrite16(info->queue_index, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_SEL);
+
+        if (info->vector != VIRTIO_MSI_NO_VECTOR)
+                free_irq(vp_dev->msix_entries[info->vector].vector, vq);
+
+        if (vp_dev->msix_enabled) {
+                iowrite16(VIRTIO_MSI_NO_VECTOR,
+                          vp_dev->ioaddr + VIRTIO_MSI_QUEUE_VECTOR);
+                /* Flush the write out to device */
+                ioread8(vp_dev->ioaddr + VIRTIO_PCI_ISR);
+        }
+
         vring_del_virtqueue(vq);
 
         /* Select and deactivate the queue */
-        iowrite16(info->queue_index, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_SEL);
         iowrite32(0, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);
 
         size = PAGE_ALIGN(vring_size(info->num, VIRTIO_PCI_VRING_ALIGN));
@@ -304,30 +486,46 @@ static void vp_del_vq(struct virtqueue *vq)
         kfree(info);
 }
 
+/* the config->del_vqs() implementation */
 static void vp_del_vqs(struct virtio_device *vdev)
 {
         struct virtqueue *vq, *n;
 
         list_for_each_entry_safe(vq, n, &vdev->vqs, list)
                 vp_del_vq(vq);
+
+        vp_free_vectors(vdev);
 }
 
+/* the config->find_vqs() implementation */
 static int vp_find_vqs(struct virtio_device *vdev, unsigned nvqs,
                        struct virtqueue *vqs[],
                        vq_callback_t *callbacks[],
                        const char *names[])
 {
-        int i;
+        int vectors = 0;
+        int i, err;
+
+        /* How many vectors would we like? */
+        for (i = 0; i < nvqs; ++i)
+                if (callbacks[i])
+                        ++vectors;
+
+        err = vp_request_vectors(vdev, vectors);
+        if (err)
+                goto error_request;
 
         for (i = 0; i < nvqs; ++i) {
                 vqs[i] = vp_find_vq(vdev, i, callbacks[i], names[i]);
                 if (IS_ERR(vqs[i]))
-                        goto error;
+                        goto error_find;
         }
         return 0;
 
-error:
+error_find:
         vp_del_vqs(vdev);
+
+error_request:
         return PTR_ERR(vqs[i]);
 }
 
@@ -349,7 +547,7 @@ static void virtio_pci_release_dev(struct device *_d)
         struct virtio_pci_device *vp_dev = to_vp_device(dev);
         struct pci_dev *pci_dev = vp_dev->pci_dev;
 
-        free_irq(pci_dev->irq, vp_dev);
+        vp_del_vqs(dev);
         pci_set_drvdata(pci_dev, NULL);
         pci_iounmap(pci_dev, vp_dev->ioaddr);
         pci_release_regions(pci_dev);
@@ -408,21 +606,13 @@ static int __devinit virtio_pci_probe(struct pci_dev *pci_dev,
         vp_dev->vdev.id.vendor = pci_dev->subsystem_vendor;
         vp_dev->vdev.id.device = pci_dev->subsystem_device;
 
-        /* register a handler for the queue with the PCI device's interrupt */
-        err = request_irq(vp_dev->pci_dev->irq, vp_interrupt, IRQF_SHARED,
-                          dev_name(&vp_dev->vdev.dev), vp_dev);
-        if (err)
-                goto out_set_drvdata;
-
         /* finally register the virtio device */
         err = register_virtio_device(&vp_dev->vdev);
         if (err)
-                goto out_req_irq;
+                goto out_set_drvdata;
 
         return 0;
 
-out_req_irq:
-        free_irq(pci_dev->irq, vp_dev);
 out_set_drvdata:
         pci_set_drvdata(pci_dev, NULL);
         pci_iounmap(pci_dev, vp_dev->ioaddr);