vfio/pci: Use xarray for interrupt context storage

Interrupt context is statically allocated at the time interrupts
are allocated. Following allocation, the context is managed by
directly accessing the elements of the array using the vector
as index. The storage is released when interrupts are disabled.

It is possible to dynamically allocate a single MSI-X interrupt
after MSI-X is enabled. A dynamic storage for interrupt context
is needed to support this. Replace the interrupt context array with an
xarray (similar to what the core uses as store for MSI descriptors)
that can support the dynamic expansion while maintaining the
custom that uses the vector as index.

With a dynamic storage it is no longer required to pre-allocate
interrupt contexts at the time the interrupts are allocated.
MSI and MSI-X interrupt contexts are only used when interrupts are
enabled. Their allocation can thus be delayed until interrupt enabling.
Only enabled interrupts will have associated interrupt contexts.
Whether an interrupt has been allocated (a Linux irq number exists
for it) becomes the criteria for whether an interrupt can be enabled.

Signed-off-by: Reinette Chatre <[email protected]>
Link: https://lore.kernel.org/lkml/[email protected]/
Reviewed-by: Kevin Tian <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Link: https://lore.kernel.org/r/40e235f38d427aff79ae35eda0ced42502aa0937.1683740667.git.reinette.chatre@intel.com
Signed-off-by: Alex Williamson <[email protected]>

Author: rchatre

drivers/vfio/pci/vfio_pci_core.c

@@ -2102,6 +2102,7 @@ int vfio_pci_core_init_dev(struct vfio_device *core_vdev)
 	INIT_LIST_HEAD(&vdev->vma_list);
 	INIT_LIST_HEAD(&vdev->sriov_pfs_item);
 	init_rwsem(&vdev->memory_lock);
+	xa_init(&vdev->ctx);
 
 	return 0;
 }

drivers/vfio/pci/vfio_pci_intrs.c

@@ -52,25 +52,33 @@ static
 struct vfio_pci_irq_ctx *vfio_irq_ctx_get(struct vfio_pci_core_device *vdev,
 					  unsigned long index)
 {
-	if (index >= vdev->num_ctx)
-		return NULL;
-	return &vdev->ctx[index];
+	return xa_load(&vdev->ctx, index);
 }
 
-static void vfio_irq_ctx_free_all(struct vfio_pci_core_device *vdev)
+static void vfio_irq_ctx_free(struct vfio_pci_core_device *vdev,
+			      struct vfio_pci_irq_ctx *ctx, unsigned long index)
 {
-	kfree(vdev->ctx);
+	xa_erase(&vdev->ctx, index);
+	kfree(ctx);
 }
 
-static int vfio_irq_ctx_alloc_num(struct vfio_pci_core_device *vdev,
-				  unsigned long num)
+static struct vfio_pci_irq_ctx *
+vfio_irq_ctx_alloc(struct vfio_pci_core_device *vdev, unsigned long index)
 {
-	vdev->ctx = kcalloc(num, sizeof(struct vfio_pci_irq_ctx),
-			    GFP_KERNEL_ACCOUNT);
-	if (!vdev->ctx)
-		return -ENOMEM;
+	struct vfio_pci_irq_ctx *ctx;
+	int ret;
 
-	return 0;
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
+	if (!ctx)
+		return NULL;
+
+	ret = xa_insert(&vdev->ctx, index, ctx, GFP_KERNEL_ACCOUNT);
+	if (ret) {
+		kfree(ctx);
+		return NULL;
+	}
+
+	return ctx;
 }
 
 /*
@@ -226,23 +234,16 @@ static irqreturn_t vfio_intx_handler(int irq, void *dev_id)
 static int vfio_intx_enable(struct vfio_pci_core_device *vdev)
 {
 	struct vfio_pci_irq_ctx *ctx;
-	int ret;
 
 	if (!is_irq_none(vdev))
 		return -EINVAL;
 
 	if (!vdev->pdev->irq)
 		return -ENODEV;
 
-	ret = vfio_irq_ctx_alloc_num(vdev, 1);
-	if (ret)
-		return ret;
-
-	ctx = vfio_irq_ctx_get(vdev, 0);
-	if (!ctx) {
-		vfio_irq_ctx_free_all(vdev);
-		return -EINVAL;
-	}
+	ctx = vfio_irq_ctx_alloc(vdev, 0);
+	if (!ctx)
+		return -ENOMEM;
 
 	vdev->num_ctx = 1;
 
@@ -334,7 +335,7 @@ static void vfio_intx_disable(struct vfio_pci_core_device *vdev)
 	vfio_intx_set_signal(vdev, -1);
 	vdev->irq_type = VFIO_PCI_NUM_IRQS;
 	vdev->num_ctx = 0;
-	vfio_irq_ctx_free_all(vdev);
+	vfio_irq_ctx_free(vdev, ctx, 0);
 }
 
 /*
@@ -358,18 +359,13 @@ static int vfio_msi_enable(struct vfio_pci_core_device *vdev, int nvec, bool msi
 	if (!is_irq_none(vdev))
 		return -EINVAL;
 
-	ret = vfio_irq_ctx_alloc_num(vdev, nvec);
-	if (ret)
-		return ret;
-
 	/* return the number of supported vectors if we can't get all: */
 	cmd = vfio_pci_memory_lock_and_enable(vdev);
 	ret = pci_alloc_irq_vectors(pdev, 1, nvec, flag);
 	if (ret < nvec) {
 		if (ret > 0)
 			pci_free_irq_vectors(pdev);
 		vfio_pci_memory_unlock_and_restore(vdev, cmd);
-		vfio_irq_ctx_free_all(vdev);
 		return ret;
 	}
 	vfio_pci_memory_unlock_and_restore(vdev, cmd);
@@ -401,29 +397,36 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
 	if (vector >= vdev->num_ctx)
 		return -EINVAL;
 
-	ctx = vfio_irq_ctx_get(vdev, vector);
-	if (!ctx)
-		return -EINVAL;
 	irq = pci_irq_vector(pdev, vector);
+	if (irq < 0)
+		return -EINVAL;
 
-	if (ctx->trigger) {
+	ctx = vfio_irq_ctx_get(vdev, vector);
+
+	if (ctx) {
 		irq_bypass_unregister_producer(&ctx->producer);
 
 		cmd = vfio_pci_memory_lock_and_enable(vdev);
 		free_irq(irq, ctx->trigger);
 		vfio_pci_memory_unlock_and_restore(vdev, cmd);
 		kfree(ctx->name);
 		eventfd_ctx_put(ctx->trigger);
-		ctx->trigger = NULL;
+		vfio_irq_ctx_free(vdev, ctx, vector);
 	}
 
 	if (fd < 0)
 		return 0;
 
+	ctx = vfio_irq_ctx_alloc(vdev, vector);
+	if (!ctx)
+		return -ENOMEM;
+
 	ctx->name = kasprintf(GFP_KERNEL_ACCOUNT, "vfio-msi%s[%d](%s)",
 			      msix ? "x" : "", vector, pci_name(pdev));
-	if (!ctx->name)
-		return -ENOMEM;
+	if (!ctx->name) {
+		ret = -ENOMEM;
+		goto out_free_ctx;
+	}
 
 	trigger = eventfd_ctx_fdget(fd);
 	if (IS_ERR(trigger)) {
@@ -469,6 +472,8 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
 	eventfd_ctx_put(trigger);
 out_free_name:
 	kfree(ctx->name);
+out_free_ctx:
+	vfio_irq_ctx_free(vdev, ctx, vector);
 	return ret;
 }
 
@@ -498,16 +503,13 @@ static void vfio_msi_disable(struct vfio_pci_core_device *vdev, bool msix)
 {
 	struct pci_dev *pdev = vdev->pdev;
 	struct vfio_pci_irq_ctx *ctx;
-	unsigned int i;
+	unsigned long i;
 	u16 cmd;
 
-	for (i = 0; i < vdev->num_ctx; i++) {
-		ctx = vfio_irq_ctx_get(vdev, i);
-		if (ctx) {
-			vfio_virqfd_disable(&ctx->unmask);
-			vfio_virqfd_disable(&ctx->mask);
-			vfio_msi_set_vector_signal(vdev, i, -1, msix);
-		}
+	xa_for_each(&vdev->ctx, i, ctx) {
+		vfio_virqfd_disable(&ctx->unmask);
+		vfio_virqfd_disable(&ctx->mask);
+		vfio_msi_set_vector_signal(vdev, i, -1, msix);
 	}
 
 	cmd = vfio_pci_memory_lock_and_enable(vdev);
@@ -523,7 +525,6 @@ static void vfio_msi_disable(struct vfio_pci_core_device *vdev, bool msix)
 
 	vdev->irq_type = VFIO_PCI_NUM_IRQS;
 	vdev->num_ctx = 0;
-	vfio_irq_ctx_free_all(vdev);
 }
 
 /*
@@ -663,7 +664,7 @@ static int vfio_pci_set_msi_trigger(struct vfio_pci_core_device *vdev,
 
 	for (i = start; i < start + count; i++) {
 		ctx = vfio_irq_ctx_get(vdev, i);
-		if (!ctx || !ctx->trigger)
+		if (!ctx)
 			continue;
 		if (flags & VFIO_IRQ_SET_DATA_NONE) {
 			eventfd_signal(ctx->trigger, 1);

include/linux/vfio_pci_core.h

@@ -59,7 +59,7 @@ struct vfio_pci_core_device {
 	struct perm_bits	*msi_perm;
 	spinlock_t		irqlock;
 	struct mutex		igate;
-	struct vfio_pci_irq_ctx	*ctx;
+	struct xarray		ctx;
 	int			num_ctx;
 	int			irq_type;
 	int			num_regions;