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Subject[PATCH v6 3/3] vfio/pci: make use of irq_update_devid() and optimize irq ops
Date
When userspace (e.g. qemu) triggers a switch between KVM
irqfd and userspace eventfd, only dev_id of irqaction
(i.e. the "trigger" in this patch's context) will be
changed, but a free-then-request-irq action is taken in
current code. And, interrupt affinity setting in VM will
also trigger a free-then-request-irq action, which actually
changes nothing in irqaction.

This patch makes use of irq_update_devid() and optimize
both cases above, which reduces the risk of losing interrupt
and also cuts some overhead.

Signed-off-by: Ben Luo <luoben@linux.alibaba.com>
---
drivers/vfio/pci/vfio_pci_intrs.c | 118 ++++++++++++++++++++++++++------------
1 file changed, 81 insertions(+), 37 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index 3fa3f72..57b2de3 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -284,8 +284,8 @@ static int vfio_msi_enable(struct vfio_pci_device *vdev, int nvec, bool msix)
static int vfio_msi_set_vector_signal(struct vfio_pci_device *vdev,
int vector, int fd, bool msix)
{
+ struct eventfd_ctx *trigger = NULL;
struct pci_dev *pdev = vdev->pdev;
- struct eventfd_ctx *trigger;
int irq, ret;

if (vector < 0 || vector >= vdev->num_ctx)
@@ -293,61 +293,105 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_device *vdev,

irq = pci_irq_vector(pdev, vector);

+ if (fd >= 0)
+ trigger = eventfd_ctx_fdget(fd);
+
+ /*
+ * 'trigger' is NULL or invalid, disable the interrupt
+ * 'trigger' is same as before, only bounce the bypass registration
+ * 'trigger' is a new valid one, update it to irqaction and other
+ * data structures referencing to the old one; fallback to disable
+ * the interrupt on error
+ */
if (vdev->ctx[vector].trigger) {
- free_irq(irq, vdev->ctx[vector].trigger);
+ /*
+ * even if the trigger is unchanged, we need to bounce the
+ * interrupt bypass connection to allow affinity changes in
+ * the guest to be realized.
+ */
irq_bypass_unregister_producer(&vdev->ctx[vector].producer);
- kfree(vdev->ctx[vector].name);
- eventfd_ctx_put(vdev->ctx[vector].trigger);
- vdev->ctx[vector].trigger = NULL;
+
+ if (vdev->ctx[vector].trigger == trigger) {
+ /* avoid duplicated referencing to the same trigger */
+ eventfd_ctx_put(trigger);
+
+ } else if (trigger && !IS_ERR(trigger)) {
+ ret = irq_update_devid(irq,
+ vdev->ctx[vector].trigger,
+ trigger);
+ if (unlikely(ret)) {
+ dev_info(&pdev->dev,
+ "update devid of %d (token %p) failed: %d\n",
+ irq, vdev->ctx[vector].trigger, ret);
+ eventfd_ctx_put(trigger);
+ free_irq(irq, vdev->ctx[vector].trigger);
+ kfree(vdev->ctx[vector].name);
+ eventfd_ctx_put(vdev->ctx[vector].trigger);
+ vdev->ctx[vector].trigger = NULL;
+ return ret;
+ }
+ eventfd_ctx_put(vdev->ctx[vector].trigger);
+ vdev->ctx[vector].producer.token = trigger;
+ vdev->ctx[vector].trigger = trigger;
+
+ } else {
+ free_irq(irq, vdev->ctx[vector].trigger);
+ kfree(vdev->ctx[vector].name);
+ eventfd_ctx_put(vdev->ctx[vector].trigger);
+ vdev->ctx[vector].trigger = NULL;
+ }
}

if (fd < 0)
return 0;
+ else if (IS_ERR(trigger))
+ return PTR_ERR(trigger);

- vdev->ctx[vector].name = kasprintf(GFP_KERNEL, "vfio-msi%s[%d](%s)",
- msix ? "x" : "", vector,
- pci_name(pdev));
- if (!vdev->ctx[vector].name)
- return -ENOMEM;
+ if (!vdev->ctx[vector].trigger) {
+ vdev->ctx[vector].name = kasprintf(GFP_KERNEL,
+ "vfio-msi%s[%d](%s)",
+ msix ? "x" : "", vector,
+ pci_name(pdev));
+ if (!vdev->ctx[vector].name) {
+ eventfd_ctx_put(trigger);
+ return -ENOMEM;
+ }

- trigger = eventfd_ctx_fdget(fd);
- if (IS_ERR(trigger)) {
- kfree(vdev->ctx[vector].name);
- return PTR_ERR(trigger);
- }
+ /*
+ * The MSIx vector table resides in device memory which may be
+ * cleared via backdoor resets. We don't allow direct access to
+ * the vector table so even if a userspace driver attempts to
+ * save/restore around such a reset it would be unsuccessful.
+ * To avoid this, restore the cached value of the message prior
+ * to enabling.
+ */
+ if (msix) {
+ struct msi_msg msg;

- /*
- * The MSIx vector table resides in device memory which may be cleared
- * via backdoor resets. We don't allow direct access to the vector
- * table so even if a userspace driver attempts to save/restore around
- * such a reset it would be unsuccessful. To avoid this, restore the
- * cached value of the message prior to enabling.
- */
- if (msix) {
- struct msi_msg msg;
+ get_cached_msi_msg(irq, &msg);
+ pci_write_msi_msg(irq, &msg);
+ }

- get_cached_msi_msg(irq, &msg);
- pci_write_msi_msg(irq, &msg);
- }
+ ret = request_irq(irq, vfio_msihandler, 0,
+ vdev->ctx[vector].name, trigger);
+ if (ret) {
+ kfree(vdev->ctx[vector].name);
+ eventfd_ctx_put(trigger);
+ return ret;
+ }

- ret = request_irq(irq, vfio_msihandler, 0,
- vdev->ctx[vector].name, trigger);
- if (ret) {
- kfree(vdev->ctx[vector].name);
- eventfd_ctx_put(trigger);
- return ret;
+ vdev->ctx[vector].producer.token = trigger;
+ vdev->ctx[vector].producer.irq = irq;
+ vdev->ctx[vector].trigger = trigger;
}

- vdev->ctx[vector].producer.token = trigger;
- vdev->ctx[vector].producer.irq = irq;
+ /* setup bypass connection and make irte updated */
ret = irq_bypass_register_producer(&vdev->ctx[vector].producer);
if (unlikely(ret))
dev_info(&pdev->dev,
"irq bypass producer (token %p) registration fails: %d\n",
vdev->ctx[vector].producer.token, ret);

- vdev->ctx[vector].trigger = trigger;
-
return 0;
}

--
1.8.3.1
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