[Qemu-devel] [RFC v4 11/13] hw/vfio/platform: Add irqfd support

[Eric Auger <eric.auger@linaro.org>]

This patch aims at optimizing IRQ handling using irqfd framework.

Instead of handling the eventfds on user-side they are handled on
kernel side using
- the KVM irqfd framework,
- the VFIO driver virqfd framework.

the virtual IRQ completion is trapped at interrupt controller
instead of on guest 1st access to any region after IRQ hit.
This removes the need for fast/slow path swap.

Overall this brings significant performance improvements.

It depends on host kernel KVM irqfd/GSI routing capability.

Signed-off-by: Alvise Rigo <a.rigo@virtualopensystems.com>
Signed-off-by: Eric Auger <eric.auger@linaro.org>

---

v3 -> v4:
[Alvise Rigo]
Use of VFIO Platform driver v6 unmask/virqfd feature and removal
of resamplefd handler. Physical IRQ unmasking is now done in
VFIO driver.

v3:
[Eric Auger]
initial support with resamplefd handled on QEMU side since the
unmask was not supported on VFIO platform driver v5.
---
 hw/vfio/platform.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)

diff --git a/hw/vfio/platform.c b/hw/vfio/platform.c
index a5fc22b..fb0f7c9 100644
--- a/hw/vfio/platform.c
+++ b/hw/vfio/platform.c
@@ -381,6 +381,101 @@ static int vfio_populate_interrupts(VFIODevice *vbasedev)
     return 0;
 }
 
+static void vfio_enable_intp_kvm(VFIOINTp *intp)
+{
+#ifdef CONFIG_KVM
+    struct kvm_irqfd irqfd = {
+        .fd = event_notifier_get_fd(&intp->interrupt),
+        .gsi = intp->virtualID,
+        .flags = KVM_IRQFD_FLAG_RESAMPLE,
+    };
+
+    struct vfio_irq_set *irq_set;
+    int ret, argsz;
+    int32_t *pfd;
+    VFIODevice *vbasedev = &intp->vdev->vbasedev;
+
+    if (!kvm_irqfds_enabled() ||
+        !kvm_check_extension(kvm_state, KVM_CAP_IRQFD_RESAMPLE)) {
+        return;
+    }
+
+    /* Get to a known interrupt state */
+    qemu_set_fd_handler(irqfd.fd, NULL, NULL, NULL);
+    vfio_mask_irqindex(vbasedev, intp->pin);
+    intp->state = VFIO_IRQ_INACTIVE;
+    qemu_set_irq(intp->qemuirq, 0);
+
+    /* Get an eventfd for resample/unmask */
+    if (event_notifier_init(&intp->unmask, 0)) {
+        error_report("vfio: Error: event_notifier_init failed eoi");
+        goto fail;
+    }
+
+    /* KVM triggers it, VFIO listens for it */
+    irqfd.resamplefd = event_notifier_get_fd(&intp->unmask);
+
+    if (kvm_vm_ioctl(kvm_state, KVM_IRQFD, &irqfd)) {
+        error_report("vfio: Error: Failed to setup resample irqfd: %m");
+        goto fail_irqfd;
+    }
+
+    argsz = sizeof(*irq_set) + sizeof(*pfd);
+
+    irq_set = g_malloc0(argsz);
+    irq_set->argsz = argsz;
+    irq_set->flags = VFIO_IRQ_SET_DATA_EVENTFD | VFIO_IRQ_SET_ACTION_UNMASK;
+    irq_set->index = intp->pin;
+    irq_set->start = 0;
+    irq_set->count = 1;
+    pfd = (int32_t *)&irq_set->data;
+
+    *pfd = irqfd.resamplefd;
+
+    ret = ioctl(vbasedev->fd, VFIO_DEVICE_SET_IRQS, irq_set);
+    g_free(irq_set);
+    if (ret) {
+        error_report("vfio: Error: Failed to setup INTx unmask fd: %m");
+        goto fail_vfio;
+    }
+
+    /* Let'em rip */
+    vfio_unmask_irqindex(vbasedev, intp->pin);
+
+    intp->kvm_accel = true;
+
+    DPRINTF("%s irqfd pin=%d to virtID = %d fd=%d, resamplefd=%d)\n",
+            __func__, intp->pin, intp->virtualID,
+            irqfd.fd, irqfd.resamplefd);
+
+    return;
+
+fail_vfio:
+    irqfd.flags = KVM_IRQFD_FLAG_DEASSIGN;
+    kvm_vm_ioctl(kvm_state, KVM_IRQFD, &irqfd);
+fail_irqfd:
+    event_notifier_cleanup(&intp->unmask);
+fail:
+    qemu_set_fd_handler(irqfd.fd, vfio_intp_interrupt, NULL, intp);
+    vfio_unmask_irqindex(vbasedev, intp->pin);
+#endif
+}
+
+void vfio_setup_irqfd(SysBusDevice *s, int index, int virq)
+{
+    VFIOPlatformDevice *vdev = container_of(s, VFIOPlatformDevice, sbdev);
+    VFIOINTp *intp;
+
+    QLIST_FOREACH(intp, &vdev->intp_list, next) {
+        if (intp->pin == index) {
+            intp->virtualID = virq;
+            DPRINTF("enable irqfd for irq index %d (virtual IRQ %d)\n",
+                    index, virq);
+            vfio_enable_intp_kvm(intp);
+        }
+    }
+}
+
 static VFIODeviceOps vfio_platform_ops = {
     .vfio_compute_needs_reset = vfio_platform_compute_needs_reset,
     .vfio_hot_reset_multi = vfio_platform_hot_reset_multi,
-- 
1.8.3.2