[PATCH 07/17] vfio/pci: Preserve per-interrupt contexts

[Reinette Chatre]

MSI and MSI-X interrupt management for PCI passthrough devices create
a new per-interrupt context every time an interrupt is allocated,
freeing it when the interrupt is freed.

The per-interrupt context contains the properties of a particular
interrupt. Without a property that persists across interrupt allocation
and free it is acceptable to always create a new per-interrupt context.

INTx interrupt context has a "masked" property that persists across
allocation and free and thus preserves its interrupt context
across interrupt allocation and free calls.

MSI and MSI-X interrupts already remain allocated across interrupt
allocation and free requests, additionally maintaining the
individual interrupt context is a reflection of this existing
behavior and matches INTx behavior so that more code can be shared.

An additional benefit is that maintaining interrupt context supports
a potential future use case of emulated interrupts, where the
"is this interrupt emulated" is a property that needs to persist
across allocation and free requests.

Persistent interrupt contexts means that existence of per-interrupt
context no longer implies a valid trigger, pointers to freed memory
should be cleared, and a new per-interrupt context cannot be assumed
needing allocation when an interrupt is allocated.

Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
---
Note to maintainers:
This addition originally formed part of the IMS work below that mostly
ignored INTx. This work focuses on INTx, MSI, MSI-X where this addition
is relevant.
https://lore.kernel.org/lkml/cover.1696609476.git.reinette.chatre@xxxxxxxxx

 drivers/vfio/pci/vfio_pci_intrs.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index 31f73c70fcd2..7ca2b983b66e 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -427,7 +427,7 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
 
 	ctx = vfio_irq_ctx_get(vdev, vector);
 
-	if (ctx) {
+	if (ctx && ctx->trigger) {
 		irq_bypass_unregister_producer(&ctx->producer);
 		irq = pci_irq_vector(pdev, vector);
 		cmd = vfio_pci_memory_lock_and_enable(vdev);
@@ -435,8 +435,9 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
 		vfio_pci_memory_unlock_and_restore(vdev, cmd);
 		/* Interrupt stays allocated, will be freed at MSI-X disable. */
 		kfree(ctx->name);
+		ctx->name = NULL;
 		eventfd_ctx_put(ctx->trigger);
-		vfio_irq_ctx_free(vdev, ctx, vector);
+		ctx->trigger = NULL;
 	}
 
 	if (fd < 0)
@@ -449,16 +450,17 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_core_device *vdev,
 			return irq;
 	}
 
-	ctx = vfio_irq_ctx_alloc(vdev, vector);
-	if (!ctx)
-		return -ENOMEM;
+	/* Per-interrupt context remain allocated. */
+	if (!ctx) {
+		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) {
-		ret = -ENOMEM;
-		goto out_free_ctx;
-	}
+	if (!ctx->name)
+		return -ENOMEM;
 
 	trigger = eventfd_ctx_fdget(fd);
 	if (IS_ERR(trigger)) {
@@ -502,8 +504,7 @@ 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);
+	ctx->name = NULL;
 	return ret;
 }
 
@@ -539,6 +540,7 @@ static void vfio_msi_disable(struct vfio_pci_core_device *vdev,
 		vfio_virqfd_disable(&ctx->unmask);
 		vfio_virqfd_disable(&ctx->mask);
 		vfio_msi_set_vector_signal(vdev, i, -1, index);
+		vfio_irq_ctx_free(vdev, ctx, i);
 	}
 
 	cmd = vfio_pci_memory_lock_and_enable(vdev);
@@ -694,7 +696,7 @@ 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)
+		if (!ctx || !ctx->trigger)
 			continue;
 		if (flags & VFIO_IRQ_SET_DATA_NONE) {
 			eventfd_signal(ctx->trigger);
-- 
2.34.1