virtio_pci: use shared interrupts for virtqueues

This lets IRQ layer handle dispatching IRQs to separate handlers for the
case where we don't have per-VQ MSI-X vectors, and allows us to greatly
simplify the code based on the assumption that we always have interrupt
vector 0 (legacy INTx or config interrupt for MSI-X) available, and
any other interrupt is request/freed throught the VQ, even if the
actual interrupt line might be shared in some cases.

This allows removing a great deal of variables keeping track of the
interrupt state in struct virtio_pci_device, as we can now simply walk the
list of VQs and deal with per-VQ interrupt handlers there, and only treat
vector 0 special.

Additionally clean up the VQ allocation code to properly unwind on error
instead of having a single global cleanup label, which is error prone,
and in this case also leads to more code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 106 insertions, 145 deletions

diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
index a33767318cbf..274dc1ff09c0 100644
--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c
@@ -33,10 +33,8 @@ void vp_synchronize_vectors(struct virtio_device *vdev)
         struct virtio_pci_device *vp_dev = to_vp_device(vdev);
         int i;
 
-        if (vp_dev->intx_enabled)
-                synchronize_irq(vp_dev->pci_dev->irq);
-
-        for (i = 0; i < vp_dev->msix_vectors; ++i)
+        synchronize_irq(pci_irq_vector(vp_dev->pci_dev, 0));
+        for (i = 1; i < vp_dev->msix_vectors; i++)
                 synchronize_irq(pci_irq_vector(vp_dev->pci_dev, i));
 }
 
@@ -99,77 +97,10 @@ static irqreturn_t vp_interrupt(int irq, void *opaque)
         return vp_vring_interrupt(irq, opaque);
 }
 
-static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
-                                   bool per_vq_vectors)
-{
-        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;
-
-        vp_dev->msix_vectors = nvectors;
-
-        vp_dev->msix_names = kmalloc(nvectors * sizeof *vp_dev->msix_names,
-                                     GFP_KERNEL);
-        if (!vp_dev->msix_names)
-                goto error;
-        vp_dev->msix_affinity_masks
-                = kzalloc(nvectors * sizeof *vp_dev->msix_affinity_masks,
-                          GFP_KERNEL);
-        if (!vp_dev->msix_affinity_masks)
-                goto error;
-        for (i = 0; i < nvectors; ++i)
-                if (!alloc_cpumask_var(&vp_dev->msix_affinity_masks[i],
-                                        GFP_KERNEL))
-                        goto error;
-
-        err = pci_alloc_irq_vectors(vp_dev->pci_dev, nvectors, nvectors,
-                        PCI_IRQ_MSIX);
-        if (err < 0)
-                goto error;
-        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(pci_irq_vector(vp_dev->pci_dev, v),
-                          vp_config_changed, 0, vp_dev->msix_names[v],
-                          vp_dev);
-        if (err)
-                goto error;
-        ++vp_dev->msix_used_vectors;
-
-        v = vp_dev->config_vector(vp_dev, v);
-        /* Verify we had enough resources to assign the vector */
-        if (v == VIRTIO_MSI_NO_VECTOR) {
-                err = -EBUSY;
-                goto error;
-        }
-
-        if (!per_vq_vectors) {
-                /* 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(pci_irq_vector(vp_dev->pci_dev, v),
-                                  vp_vring_interrupt, 0, vp_dev->msix_names[v],
-                                  vp_dev);
-                if (err)
-                        goto error;
-                ++vp_dev->msix_used_vectors;
-        }
-        return 0;
-error:
-        return err;
-}
-
-/* the config->del_vqs() implementation */
-void vp_del_vqs(struct virtio_device *vdev)
+static void vp_remove_vqs(struct virtio_device *vdev)
 {
         struct virtio_pci_device *vp_dev = to_vp_device(vdev);
         struct virtqueue *vq, *n;
-        int i;
 
         list_for_each_entry_safe(vq, n, &vdev->vqs, list) {
                 if (vp_dev->msix_vector_map) {
@@ -181,35 +112,33 @@ void vp_del_vqs(struct virtio_device *vdev)
                 }
                 vp_dev->del_vq(vq);
         }
+}
 
-        if (vp_dev->intx_enabled) {
-                free_irq(vp_dev->pci_dev->irq, vp_dev);
-                vp_dev->intx_enabled = 0;
-        }
+/* the config->del_vqs() implementation */
+void vp_del_vqs(struct virtio_device *vdev)
+{
+        struct virtio_pci_device *vp_dev = to_vp_device(vdev);
+        int i;
 
-        for (i = 0; i < vp_dev->msix_used_vectors; ++i)
-                free_irq(pci_irq_vector(vp_dev->pci_dev, i), vp_dev);
+        if (WARN_ON_ONCE(list_empty_careful(&vdev->vqs)))
+                return;
 
-        for (i = 0; i < vp_dev->msix_vectors; i++)
-                if (vp_dev->msix_affinity_masks[i])
-                        free_cpumask_var(vp_dev->msix_affinity_masks[i]);
+        vp_remove_vqs(vdev);
 
         if (vp_dev->msix_enabled) {
+                for (i = 0; i < vp_dev->msix_vectors; i++)
+                        free_cpumask_var(vp_dev->msix_affinity_masks[i]);
+
                 /* Disable the vector used for configuration */
                 vp_dev->config_vector(vp_dev, VIRTIO_MSI_NO_VECTOR);
 
-                pci_free_irq_vectors(vp_dev->pci_dev);
-                vp_dev->msix_enabled = 0;
+                kfree(vp_dev->msix_affinity_masks);
+                kfree(vp_dev->msix_names);
+                kfree(vp_dev->msix_vector_map);
         }
 
-        vp_dev->msix_vectors = 0;
-        vp_dev->msix_used_vectors = 0;
-        kfree(vp_dev->msix_names);
-        vp_dev->msix_names = NULL;
-        kfree(vp_dev->msix_affinity_masks);
-        vp_dev->msix_affinity_masks = NULL;
-        kfree(vp_dev->msix_vector_map);
-        vp_dev->msix_vector_map = NULL;
+        free_irq(pci_irq_vector(vp_dev->pci_dev, 0), vp_dev);
+        pci_free_irq_vectors(vp_dev->pci_dev);
 }
 
 static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned nvqs,
@@ -219,79 +148,122 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned nvqs,
                               bool per_vq_vectors)
 {
         struct virtio_pci_device *vp_dev = to_vp_device(vdev);
+        const char *name = dev_name(&vp_dev->vdev.dev);
+        int i, err = -ENOMEM, allocated_vectors, nvectors;
         u16 msix_vec;
-        int i, err, nvectors, allocated_vectors;
+
+        nvectors = 1;
+        for (i = 0; i < nvqs; i++)
+                if (callbacks[i])
+                        nvectors++;
 
         if (per_vq_vectors) {
-                /* Best option: one for change interrupt, one per vq. */
-                nvectors = 1;
-                for (i = 0; i < nvqs; ++i)
-                        if (callbacks[i])
-                                ++nvectors;
+                err = pci_alloc_irq_vectors(vp_dev->pci_dev, nvectors, nvectors,
+                                PCI_IRQ_MSIX);
         } else {
-                /* Second best: one for change, shared for all vqs. */
-                nvectors = 2;
+                err = pci_alloc_irq_vectors(vp_dev->pci_dev, 2, 2,
+                                PCI_IRQ_MSIX);
         }
+        if (err < 0)
+                return err;
 
-        err = vp_request_msix_vectors(vdev, nvectors, per_vq_vectors);
+        vp_dev->msix_vectors = nvectors;
+        vp_dev->msix_names = kmalloc_array(nvectors,
+                        sizeof(*vp_dev->msix_names), GFP_KERNEL);
+        if (!vp_dev->msix_names)
+                goto out_free_irq_vectors;
+
+        vp_dev->msix_affinity_masks = kcalloc(nvectors,
+                        sizeof(*vp_dev->msix_affinity_masks), GFP_KERNEL);
+        if (!vp_dev->msix_affinity_masks)
+                goto out_free_msix_names;
+
+        for (i = 0; i < nvectors; ++i) {
+                if (!alloc_cpumask_var(&vp_dev->msix_affinity_masks[i],
+                                GFP_KERNEL))
+                        goto out_free_msix_affinity_masks;
+        }
+
+        /* Set the vector used for configuration */
+        snprintf(vp_dev->msix_names[0], sizeof(*vp_dev->msix_names),
+                 "%s-config", name);
+        err = request_irq(pci_irq_vector(vp_dev->pci_dev, 0), vp_config_changed,
+                        0, vp_dev->msix_names[0], vp_dev);
         if (err)
-                goto error_find;
+                goto out_free_irq_vectors;
 
-        if (per_vq_vectors) {
-                vp_dev->msix_vector_map = kmalloc_array(nvqs,
-                                sizeof(*vp_dev->msix_vector_map), GFP_KERNEL);
-                if (!vp_dev->msix_vector_map)
-                        goto error_find;
+        /* Verify we had enough resources to assign the vector */
+        if (vp_dev->config_vector(vp_dev, 0) == VIRTIO_MSI_NO_VECTOR) {
+                err = -EBUSY;
+                goto out_free_config_irq;
         }
 
-        allocated_vectors = vp_dev->msix_used_vectors;
+        vp_dev->msix_vector_map = kmalloc_array(nvqs,
+                        sizeof(*vp_dev->msix_vector_map), GFP_KERNEL);
+        if (!vp_dev->msix_vector_map)
+                goto out_disable_config_irq;
+
+        allocated_vectors = 1; /* vector 0 is the config interrupt */
         for (i = 0; i < nvqs; ++i) {
                 if (!names[i]) {
                         vqs[i] = NULL;
                         continue;
                 }
 
-                if (!callbacks[i])
-                        msix_vec = VIRTIO_MSI_NO_VECTOR;
-                else if (per_vq_vectors)
-                        msix_vec = allocated_vectors++;
+                if (callbacks[i])
+                        msix_vec = allocated_vectors;
                 else
-                        msix_vec = VP_MSIX_VQ_VECTOR;
+                        msix_vec = VIRTIO_MSI_NO_VECTOR;
+
                 vqs[i] = vp_dev->setup_vq(vp_dev, i, callbacks[i], names[i],
                                 msix_vec);
                 if (IS_ERR(vqs[i])) {
                         err = PTR_ERR(vqs[i]);
-                        goto error_find;
+                        goto out_remove_vqs;
                 }
 
-                if (!per_vq_vectors)
-                        continue;
-
                 if (msix_vec == VIRTIO_MSI_NO_VECTOR) {
                         vp_dev->msix_vector_map[i] = VIRTIO_MSI_NO_VECTOR;
                         continue;
                 }
 
-                /* allocate per-vq irq if available and necessary */
-                snprintf(vp_dev->msix_names[msix_vec],
-                         sizeof *vp_dev->msix_names,
-                         "%s-%s",
+                snprintf(vp_dev->msix_names[i + 1],
+                         sizeof(*vp_dev->msix_names), "%s-%s",
                          dev_name(&vp_dev->vdev.dev), names[i]);
                 err = request_irq(pci_irq_vector(vp_dev->pci_dev, msix_vec),
-                                  vring_interrupt, 0,
-                                  vp_dev->msix_names[msix_vec],
-                                  vqs[i]);
+                                  vring_interrupt, IRQF_SHARED,
+                                  vp_dev->msix_names[i + 1], vqs[i]);
                 if (err) {
                         /* don't free this irq on error */
                         vp_dev->msix_vector_map[i] = VIRTIO_MSI_NO_VECTOR;
-                        goto error_find;
+                        goto out_remove_vqs;
                 }
                 vp_dev->msix_vector_map[i] = msix_vec;
+
+                if (per_vq_vectors)
+                        allocated_vectors++;
         }
+
+        vp_dev->msix_enabled = 1;
         return 0;
 
-error_find:
-        vp_del_vqs(vdev);
+out_remove_vqs:
+        vp_remove_vqs(vdev);
+        kfree(vp_dev->msix_vector_map);
+out_disable_config_irq:
+        vp_dev->config_vector(vp_dev, VIRTIO_MSI_NO_VECTOR);
+out_free_config_irq:
+        free_irq(pci_irq_vector(vp_dev->pci_dev, 0), vp_dev);
+out_free_msix_affinity_masks:
+        for (i = 0; i < nvectors; i++) {
+                if (vp_dev->msix_affinity_masks[i])
+                        free_cpumask_var(vp_dev->msix_affinity_masks[i]);
+        }
+        kfree(vp_dev->msix_affinity_masks);
+out_free_msix_names:
+        kfree(vp_dev->msix_names);
+out_free_irq_vectors:
+        pci_free_irq_vectors(vp_dev->pci_dev);
         return err;
 }
 
@@ -305,9 +277,8 @@ static int vp_find_vqs_intx(struct virtio_device *vdev, unsigned nvqs,
         err = request_irq(vp_dev->pci_dev->irq, vp_interrupt, IRQF_SHARED,
                         dev_name(&vdev->dev), vp_dev);
         if (err)
-                goto out_del_vqs;
+                return err;
 
-        vp_dev->intx_enabled = 1;
         for (i = 0; i < nvqs; ++i) {
                 if (!names[i]) {
                         vqs[i] = NULL;
@@ -317,13 +288,15 @@ static int vp_find_vqs_intx(struct virtio_device *vdev, unsigned nvqs,
                                 VIRTIO_MSI_NO_VECTOR);
                 if (IS_ERR(vqs[i])) {
                         err = PTR_ERR(vqs[i]);
-                        goto out_del_vqs;
+                        goto out_remove_vqs;
                 }
         }
 
         return 0;
-out_del_vqs:
-        vp_del_vqs(vdev);
+
+out_remove_vqs:
+        vp_remove_vqs(vdev);
+        free_irq(pci_irq_vector(vp_dev->pci_dev, 0), vp_dev);
         return err;
 }
 
diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h
index 2038887bdf23..85593867e712 100644
--- a/drivers/virtio/virtio_pci_common.h
+++ b/drivers/virtio/virtio_pci_common.h
@@ -66,16 +66,12 @@ struct virtio_pci_device {
 
         /* MSI-X support */
         int msix_enabled;
-        int intx_enabled;
         cpumask_var_t *msix_affinity_masks;
         /* 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, excluding per-vq vectors if any */
-        unsigned msix_used_vectors;
-
+        /* Total Number of MSI-X vectors (including per-VQ ones). */
+        int msix_vectors;
         /* Map of per-VQ MSI-X vectors, may be NULL */
         unsigned *msix_vector_map;
 
@@ -89,14 +85,6 @@ struct virtio_pci_device {
         u16 (*config_vector)(struct virtio_pci_device *vp_dev, u16 vector);
 };
 
-/* 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,
-};
-
 /* Convert a generic virtio device to our structure */
 static struct virtio_pci_device *to_vp_device(struct virtio_device *vdev)
 {