hw/vfio/platform: add irqfd support

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
This removes the need for fast/slow path swap.

Overall this brings significant performance improvements.

Signed-off-by: Alvise Rigo <a.rigo@virtualopensystems.com>
Signed-off-by: Eric Auger <eric.auger@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Vikram Sethi <vikrams@codeaurora.org>
Acked-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

hw/vfio/platform.c

@@ -26,6 +26,7 @@
 #include "hw/sysbus.h"
 #include "trace.h"
 #include "hw/platform-bus.h"
+#include "sysemu/kvm.h"
 
 /*
  * Functions used whatever the injection method
@@ -51,6 +52,7 @@ static VFIOINTp *vfio_init_intp(VFIODevice *vbasedev,
     intp->pin = info.index;
     intp->flags = info.flags;
     intp->state = VFIO_IRQ_INACTIVE;
+    intp->kvm_accel = false;
 
     sysbus_init_irq(sbdev, &intp->qemuirq);
 
@@ -61,6 +63,13 @@ static VFIOINTp *vfio_init_intp(VFIODevice *vbasedev,
         error_report("vfio: Error: trigger event_notifier_init failed ");
         return NULL;
     }
+    /* Get an eventfd for resample/unmask */
+    ret = event_notifier_init(&intp->unmask, 0);
+    if (ret) {
+        g_free(intp);
+        error_report("vfio: Error: resamplefd event_notifier_init failed");
+        return NULL;
+    }
 
     QLIST_INSERT_HEAD(&vdev->intp_list, intp, next);
     return intp;
@@ -315,6 +324,94 @@ static int vfio_start_eventfd_injection(VFIOINTp *intp)
     return ret;
 }
 
+/*
+ * Functions used for irqfd
+ */
+
+/**
+ * vfio_set_resample_eventfd - sets the resamplefd for an IRQ
+ * @intp: the IRQ struct handle
+ * programs the VFIO driver to unmask this IRQ when the
+ * intp->unmask eventfd is triggered
+ */
+static int vfio_set_resample_eventfd(VFIOINTp *intp)
+{
+    VFIODevice *vbasedev = &intp->vdev->vbasedev;
+    struct vfio_irq_set *irq_set;
+    int argsz, ret;
+    int32_t *pfd;
+
+    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 = event_notifier_get_fd(&intp->unmask);
+    qemu_set_fd_handler(*pfd, NULL, NULL, NULL);
+    ret = ioctl(vbasedev->fd, VFIO_DEVICE_SET_IRQS, irq_set);
+    g_free(irq_set);
+    if (ret < 0) {
+        error_report("vfio: Failed to set resample eventfd: %m");
+    }
+    return ret;
+}
+
+static void vfio_start_irqfd_injection(SysBusDevice *sbdev, qemu_irq irq)
+{
+    VFIOPlatformDevice *vdev = VFIO_PLATFORM_DEVICE(sbdev);
+    VFIOINTp *intp;
+
+    if (!kvm_irqfds_enabled() || !kvm_resamplefds_enabled() ||
+        !vdev->irqfd_allowed) {
+        return;
+    }
+
+    QLIST_FOREACH(intp, &vdev->intp_list, next) {
+        if (intp->qemuirq == irq) {
+            break;
+        }
+    }
+    assert(intp);
+
+    /* Get to a known interrupt state */
+    qemu_set_fd_handler(event_notifier_get_fd(&intp->interrupt),
+                        NULL, NULL, vdev);
+
+    vfio_mask_single_irqindex(&vdev->vbasedev, intp->pin);
+    qemu_set_irq(intp->qemuirq, 0);
+
+    if (kvm_irqchip_add_irqfd_notifier(kvm_state, &intp->interrupt,
+                                   &intp->unmask, irq) < 0) {
+        goto fail_irqfd;
+    }
+
+    if (vfio_set_trigger_eventfd(intp, NULL) < 0) {
+        goto fail_vfio;
+    }
+    if (vfio_set_resample_eventfd(intp) < 0) {
+        goto fail_vfio;
+    }
+
+    /* Let's resume injection with irqfd setup */
+    vfio_unmask_single_irqindex(&vdev->vbasedev, intp->pin);
+
+    intp->kvm_accel = true;
+
+    trace_vfio_platform_start_irqfd_injection(intp->pin,
+                                     event_notifier_get_fd(&intp->interrupt),
+                                     event_notifier_get_fd(&intp->unmask));
+    return;
+fail_vfio:
+    kvm_irqchip_remove_irqfd_notifier(kvm_state, &intp->interrupt, irq);
+fail_irqfd:
+    vfio_start_eventfd_injection(intp);
+    vfio_unmask_single_irqindex(&vdev->vbasedev, intp->pin);
+    return;
+}
+
 /* VFIO skeleton */
 
 static void vfio_platform_compute_needs_reset(VFIODevice *vbasedev)
@@ -584,17 +681,20 @@ static Property vfio_platform_dev_properties[] = {
     DEFINE_PROP_BOOL("x-mmap", VFIOPlatformDevice, vbasedev.allow_mmap, true),
     DEFINE_PROP_UINT32("mmap-timeout-ms", VFIOPlatformDevice,
                        mmap_timeout, 1100),
+    DEFINE_PROP_BOOL("x-irqfd", VFIOPlatformDevice, irqfd_allowed, true),
     DEFINE_PROP_END_OF_LIST(),
 };
 
 static void vfio_platform_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
+    SysBusDeviceClass *sbc = SYS_BUS_DEVICE_CLASS(klass);
 
     dc->realize = vfio_platform_realize;
     dc->props = vfio_platform_dev_properties;
     dc->vmsd = &vfio_platform_vmstate;
     dc->desc = "VFIO-based platform device assignment";
+    sbc->connect_irq_notifier = vfio_start_irqfd_injection;
     set_bit(DEVICE_CATEGORY_MISC, dc->categories);
 }
 

include/hw/vfio/vfio-platform.h

@@ -41,6 +41,7 @@ typedef struct VFIOINTp {
     int state; /* inactive, pending, active */
     uint8_t pin; /* index */
     uint32_t flags; /* IRQ info flags */
+    bool kvm_accel; /* set when QEMU bypass through KVM enabled */
 } VFIOINTp;
 
 /* function type for user side eventfd handler */
@@ -57,6 +58,7 @@ typedef struct VFIOPlatformDevice {
     uint32_t mmap_timeout; /* delay to re-enable mmaps after interrupt */
     QEMUTimer *mmap_timer; /* allows fast-path resume after IRQ hit */
     QemuMutex intp_mutex; /* protect the intp_list IRQ state */
+    bool irqfd_allowed; /* debug option to force irqfd on/off */
 } VFIOPlatformDevice;
 
 typedef struct VFIOPlatformDeviceClass {

trace-events

@@ -1594,6 +1594,7 @@ vfio_platform_intp_interrupt(int pin, int fd) "Inject IRQ #%d (fd = %d)"
 vfio_platform_intp_inject_pending_lockheld(int pin, int fd) "Inject pending IRQ #%d (fd = %d)"
 vfio_platform_populate_interrupts(int pin, int count, int flags) "- IRQ index %d: count %d, flags=0x%x"
 vfio_intp_interrupt_set_pending(int index) "irq %d is set PENDING"
+vfio_platform_start_irqfd_injection(int index, int fd, int resamplefd) "IRQ index=%d, fd = %d, resamplefd = %d"
 
 #hw/acpi/memory_hotplug.c
 mhp_acpi_invalid_slot_selected(uint32_t slot) "0x%"PRIx32