linux-kernel - [RFC PATCH V2 16/18] vfio/pci: Support emulated interrupts in IMS backend

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Date:   Fri,  6 Oct 2023 09:41:11 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     jgg@...dia.com, yishaih@...dia.com,
        shameerali.kolothum.thodi@...wei.com, kevin.tian@...el.com,
        alex.williamson@...hat.com
Cc:     kvm@...r.kernel.org, dave.jiang@...el.com, jing2.liu@...el.com,
        ashok.raj@...el.com, fenghua.yu@...el.com,
        tom.zanussi@...ux.intel.com, reinette.chatre@...el.com,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: [RFC PATCH V2 16/18] vfio/pci: Support emulated interrupts in IMS backend

An emulated interrupt has an associated eventfd but is
not backed by a hardware interrupt.

Add support for emulated interrupts to the IMS backend
that generally involves avoiding the actions involving
hardware configuration.

Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
---
 drivers/vfio/pci/vfio_pci_intrs.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index c6b213d52beb..f96d7481094a 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -863,8 +863,8 @@ EXPORT_SYMBOL_GPL(vfio_pci_release_intr_ctx);
 /*
  * Free the IMS interrupt associated with @ctx.
  *
- * For an IMS interrupt the interrupt is freed from the underlying
- * PCI device's IMS domain.
+ * For an emulated interrupt there is nothing to do. For an IMS interrupt
+ * the interrupt is freed from the underlying PCI device's IMS domain.
  */
 static void vfio_pci_ims_irq_free(struct vfio_pci_intr_ctx *intr_ctx,
 				  struct vfio_pci_irq_ctx *ctx)
@@ -872,6 +872,9 @@ static void vfio_pci_ims_irq_free(struct vfio_pci_intr_ctx *intr_ctx,
 	struct vfio_pci_ims *ims = intr_ctx->priv;
 	struct msi_map irq_map = {};
 
+	if (ctx->emulated)
+		return;
+
 	irq_map.index = ctx->ims_id;
 	irq_map.virq = ctx->virq;
 	pci_ims_free_irq(ims->pdev, irq_map);
@@ -882,8 +885,8 @@ static void vfio_pci_ims_irq_free(struct vfio_pci_intr_ctx *intr_ctx,
 /*
  * Allocate a host IMS interrupt for @ctx.
  *
- * For an IMS interrupt the interrupt is allocated from the underlying
- * PCI device's IMS domain.
+ * For an emulated interrupt there is nothing to do. For an IMS interrupt
+ * the interrupt is allocated from the underlying PCI device's IMS domain.
  */
 static int vfio_pci_ims_irq_alloc(struct vfio_pci_intr_ctx *intr_ctx,
 				  struct vfio_pci_irq_ctx *ctx)
@@ -891,6 +894,9 @@ static int vfio_pci_ims_irq_alloc(struct vfio_pci_intr_ctx *intr_ctx,
 	struct vfio_pci_ims *ims = intr_ctx->priv;
 	struct msi_map irq_map = {};
 
+	if (ctx->emulated)
+		return -EINVAL;
+
 	irq_map = pci_ims_alloc_irq(ims->pdev, &ctx->icookie, NULL);
 	if (irq_map.index < 0)
 		return irq_map.index;
@@ -913,9 +919,11 @@ static int vfio_pci_ims_set_vector_signal(struct vfio_pci_intr_ctx *intr_ctx,
 	ctx = vfio_irq_ctx_get(intr_ctx, vector);
 
 	if (ctx && ctx->trigger) {
-		irq_bypass_unregister_producer(&ctx->producer);
-		free_irq(ctx->virq, ctx->trigger);
-		vfio_pci_ims_irq_free(intr_ctx, ctx);
+		if (!ctx->emulated) {
+			irq_bypass_unregister_producer(&ctx->producer);
+			free_irq(ctx->virq, ctx->trigger);
+			vfio_pci_ims_irq_free(intr_ctx, ctx);
+		}
 		kfree(ctx->name);
 		ctx->name = NULL;
 		eventfd_ctx_put(ctx->trigger);
@@ -945,6 +953,9 @@ static int vfio_pci_ims_set_vector_signal(struct vfio_pci_intr_ctx *intr_ctx,
 
 	ctx->trigger = trigger;
 
+	if (ctx->emulated)
+		return 0;
+
 	ret = vfio_pci_ims_irq_alloc(intr_ctx, ctx);
 	if (ret < 0)
 		goto out_put_eventfd_ctx;
@@ -1078,7 +1089,7 @@ int vfio_pci_ims_init_intr_ctx(struct vfio_device *vdev,
 
 	intr_ctx->ops = &vfio_pci_ims_intr_ops;
 	intr_ctx->priv = ims;
-	intr_ctx->supports_emulated = false;
+	intr_ctx->supports_emulated = true;
 	intr_ctx->ims_backed_irq = true;
 
 	return 0;
-- 
2.34.1