[PATCH V3 09/10] vfio/pci: Support dynamic MSI-X

[Reinette Chatre]

Recently introduced pci_msix_alloc_irq_at() and pci_msix_free_irq()
enables an individual MSI-X interrupt to be allocated and freed after
MSI-X enabling.

Use dynamic MSI-X (if supported by the device) to allocate an interrupt
after MSI-X is enabled. An MSI-X interrupt is dynamically allocated at
the time a valid eventfd is assigned. This is different behavior from
a range provided during MSI-X enabling where interrupts are allocated
for the entire range whether a valid eventfd is provided for each
interrupt or not.

Do not dynamically free interrupts, leave that to when MSI-X is
disabled.

Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Link: https://lore.kernel.org/lkml/20230403211841.0e206b67.alex.williamson@xxxxxxxxxx/
---
The get_cached_msi_msg()/pci_write_msi_msg() behavior is kept
similar to the scenario when MSI-X is enabled with triggers
provided for new interrupts. get_cached_msi_msg()/pci_write_msi_msg()
follows for interrupts recently allocated with pci_msix_alloc_irq_at()
just like get_cached_msi_msg()/pci_write_msi_msg() is done for
interrupts recently allocated with pci_alloc_irq_vectors().

Changes since V2:
- Move vfio_irq_ctx_free() to earlier in series to support
  earlier usage. (Alex)
- Use consistent terms in changelog: MSI-x changed to MSI-X.
- Make dynamic interrupt context creation generic across all
  MSI/MSI-X interrupts. This resulted in code moving to earlier
  in series as part of xarray introduction patch. (Alex)
- Remove the local allow_dyn_alloc and direct calling of
  pci_msix_can_alloc_dyn(), use the new vdev->has_dyn_msix
  introduced earlier instead. (Alex)
- Stop tracking new allocations (remove "new_ctx"). (Alex)
- Introduce new wrapper that returns Linux interrupt number or
  dynamically allocate a new interrupt. Wrapper can be used for
  all interrupt cases. (Alex)
- Only free dynamic MSI-X interrupts on MSI-X teardown. (Alex)

Changes since RFC V1:
- Add pointer to interrupt context as function parameter to
  vfio_irq_ctx_free(). (Alex)
- Initialize new_ctx to false. (Dan Carpenter)
- Only support dynamic allocation if device supports it. (Alex)

 drivers/vfio/pci/vfio_pci_intrs.c | 73 +++++++++++++++++++++++++++----
 1 file changed, 65 insertions(+), 8 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index bdda7f46c2be..c1a3e224c867 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -372,27 +372,74 @@ static int vfio_msi_enable(struct vfio_pci_core_device *vdev, int nvec, bool msi
 	return 0;
 }
 
+/*
+ * Return Linux IRQ number of an MSI or MSI-X device interrupt vector.
+ * If a Linux IRQ number is not available then a new interrupt will be
+ * allocated if dynamic MSI-X is supported.
+ */
+static int vfio_msi_alloc_irq(struct vfio_pci_core_device *vdev,
+			      unsigned int vector, bool msix)
+{
+	struct pci_dev *pdev = vdev->pdev;
+	struct msi_map map;
+	int irq;
+	u16 cmd;
+
+	irq = pci_irq_vector(pdev, vector);
+	if (irq > 0 || !msix || !vdev->has_dyn_msix)
+		return irq;
+
+	cmd = vfio_pci_memory_lock_and_enable(vdev);
+	map = pci_msix_alloc_irq_at(pdev, vector, NULL);
+	vfio_pci_memory_unlock_and_restore(vdev, cmd);
+
+	return map.index < 0 ? map.index : map.virq;
+}
+
+/*
+ * Free interrupt if it can be re-allocated dynamically (while MSI-X
+ * is enabled).
+ */
+static void vfio_msi_free_irq(struct vfio_pci_core_device *vdev,
+			      unsigned int vector, bool msix)
+{
+	struct pci_dev *pdev = vdev->pdev;
+	struct msi_map map;
+	int irq;
+	u16 cmd;
+
+	if (!msix || !vdev->has_dyn_msix)
+		return;
+
+	irq = pci_irq_vector(pdev, vector);
+	map = (struct msi_map) { .index = vector, .virq = irq };
+
+	if (WARN_ON(irq < 0))
+		return;
+
+	cmd = vfio_pci_memory_lock_and_enable(vdev);
+	pci_msix_free_irq(pdev, map);
+	vfio_pci_memory_unlock_and_restore(vdev, cmd);
+}
+
 static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
 				      unsigned int vector, int fd, bool msix)
 {
 	struct pci_dev *pdev = vdev->pdev;
 	struct vfio_pci_irq_ctx *ctx;
 	struct eventfd_ctx *trigger;
-	int irq, ret;
+	int irq = -EINVAL, ret;
 	u16 cmd;
 
-	irq = pci_irq_vector(pdev, vector);
-	if (irq < 0)
-		return -EINVAL;
-
 	ctx = vfio_irq_ctx_get(vdev, vector);
 
 	if (ctx) {
 		irq_bypass_unregister_producer(&ctx->producer);
-
+		irq = pci_irq_vector(pdev, vector);
 		cmd = vfio_pci_memory_lock_and_enable(vdev);
 		free_irq(irq, ctx->trigger);
 		vfio_pci_memory_unlock_and_restore(vdev, cmd);
+		/* Interrupt stays allocated, will be freed at MSI-X disable. */
 		kfree(ctx->name);
 		eventfd_ctx_put(ctx->trigger);
 		vfio_irq_ctx_free(vdev, ctx, vector);
@@ -401,9 +448,17 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
 	if (fd < 0)
 		return 0;
 
+	if (irq == -EINVAL) {
+		irq = vfio_msi_alloc_irq(vdev, vector, msix);
+		if (irq < 0)
+			return irq;
+	}
+
 	ctx = vfio_irq_ctx_alloc(vdev, vector);
-	if (!ctx)
-		return -ENOMEM;
+	if (!ctx) {
+		ret = -ENOMEM;
+		goto out_free_irq;
+	}
 
 	ctx->name = kasprintf(GFP_KERNEL_ACCOUNT, "vfio-msi%s[%d](%s)",
 			      msix ? "x" : "", vector, pci_name(pdev));
@@ -456,6 +511,8 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
 	kfree(ctx->name);
 out_free_ctx:
 	vfio_irq_ctx_free(vdev, ctx, vector);
+out_free_irq:
+	vfio_msi_free_irq(vdev, vector, msix);
 	return ret;
 }
 
-- 
2.34.1