Re: [PATCH v10 7/7] hw/vfio/platform: add irqfd support

["Alex Bennée" <alex.bennee@linaro.org>]

Eric Auger <eric.auger@linaro.org> writes:

> 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.
>
> it depends on host kernel KVM irqfd.
>
> 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>

>
> ---
> v5 -> v6
> - rely on kvm_irqfds_enabled() and kvm_resamplefds_enabled()
> - guard KVM code with #ifdef CONFIG_KVM
>
> 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.
>
> Conflicts:
> 	hw/vfio/platform.c
> ---
>  hw/vfio/platform.c              | 104 +++++++++++++++++++++++++++++++++++++++-
>  include/hw/vfio/vfio-platform.h |   1 +
>  trace-events                    |   2 +
>  3 files changed, 106 insertions(+), 1 deletion(-)
>
> diff --git a/hw/vfio/platform.c b/hw/vfio/platform.c
> index 30798d8..cadc824 100644
> --- a/hw/vfio/platform.c
> +++ b/hw/vfio/platform.c
> @@ -26,6 +26,7 @@
>  #include "hw/sysbus.h"
>  #include "trace.h"
>  #include "hw/platform-bus.h"
> +#include "sysemu/kvm.h"
>  
>  static void vfio_intp_interrupt(VFIOINTp *intp);
>  typedef void (*eventfd_user_side_handler_t)(VFIOINTp *intp);
> @@ -237,6 +238,83 @@ static int vfio_start_eventfd_injection(VFIOINTp *intp)
>  }
>  
>  /*
> + * Functions used for irqfd
> + */
> +
> +#ifdef CONFIG_KVM
> +
> +/**
> + * vfio_set_resample_eventfd - sets the resamplefd for an IRQ
> + * @intp: the IRQ struct pointer
> + * 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, intp);
> +    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");
> +        qemu_set_fd_handler(*pfd, NULL, NULL, NULL);
> +    }
> +    return ret;
> +}
> +
> +/**
> + * vfio_start_irqfd_injection - starts irqfd injection for an IRQ
> + * programs VFIO driver with both the trigger and resamplefd
> + * programs KVM with the gsi, trigger & resample eventfds
> + */
> +static int vfio_start_irqfd_injection(VFIOINTp *intp)
> +{
> +    struct kvm_irqfd irqfd = {
> +        .fd = event_notifier_get_fd(&intp->interrupt),
> +        .resamplefd = event_notifier_get_fd(&intp->unmask),
> +        .gsi = intp->virtualID,
> +        .flags = KVM_IRQFD_FLAG_RESAMPLE,
> +    };
> +
> +    if (kvm_vm_ioctl(kvm_state, KVM_IRQFD, &irqfd)) {
> +        error_report("vfio: Error: Failed to assign the irqfd: %m");
> +        goto fail_irqfd;
> +    }
> +    if (vfio_set_trigger_eventfd(intp, NULL) < 0) {
> +        goto fail_vfio;
> +    }
> +    if (vfio_set_resample_eventfd(intp) < 0) {
> +        goto fail_vfio;
> +    }
> +
> +    intp->kvm_accel = true;
> +    trace_vfio_platform_start_irqfd_injection(intp->pin, intp->virtualID,
> +                                     irqfd.fd, irqfd.resamplefd);
> +    return 0;
> +
> +fail_vfio:
> +    irqfd.flags = KVM_IRQFD_FLAG_DEASSIGN;
> +    kvm_vm_ioctl(kvm_state, KVM_IRQFD, &irqfd);
> +fail_irqfd:
> +    return -1;
> +}
> +
> +#endif
> +
> +/*
>   * Functions used whatever the injection method
>   */
>  
> @@ -315,6 +393,13 @@ static VFIOINTp *vfio_init_intp(VFIODevice *vbasedev, unsigned int index)
>          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: resample event_notifier_init failed eoi");
> +        return NULL;
> +    }
>  
>      /* store the new intp in qlist */
>      QLIST_INSERT_HEAD(&vdev->intp_list, intp, next);
> @@ -409,7 +494,6 @@ static VFIODeviceOps vfio_platform_ops = {
>      .vfio_compute_needs_reset = vfio_platform_compute_needs_reset,
>      .vfio_hot_reset_multi = vfio_platform_hot_reset_multi,
>      .vfio_eoi = vfio_platform_eoi,
> -    .vfio_populate_device = vfio_populate_device,
>  };
>  
>  /**
> @@ -481,6 +565,13 @@ static int vfio_base_device_init(VFIODevice *vbasedev)
>          error_report("vfio: failed to get device %s", path);
>          vfio_put_group(group);
>      }
> +
> +    ret = vfio_populate_device(vbasedev);
> +    if (ret) {
> +        error_report("vfio: failed to populate device %s", path);
> +        vfio_put_group(group);
> +    }
> +
>      return ret;
>  }
>  
> @@ -536,7 +627,17 @@ static void vfio_platform_realize(DeviceState *dev, Error **errp)
>  
>      vbasedev->type = VFIO_DEVICE_TYPE_PLATFORM;
>      vbasedev->ops = &vfio_platform_ops;
> +
> +#ifdef CONFIG_KVM
> +    if (kvm_irqfds_enabled() && kvm_resamplefds_enabled() &&
> +        vdev->irqfd_allowed) {
> +        vdev->start_irq_fn = vfio_start_irqfd_injection;
> +    } else {
> +        vdev->start_irq_fn = vfio_start_eventfd_injection;
> +    }
> +#else
>      vdev->start_irq_fn = vfio_start_eventfd_injection;
> +#endif
>  
>      trace_vfio_platform_realize(vbasedev->name, vdev->compat);
>  
> @@ -614,6 +715,7 @@ static Property vfio_platform_dev_properties[] = {
>      DEFINE_PROP_STRING("host", VFIOPlatformDevice, vbasedev.name),
>      DEFINE_PROP_UINT32("mmap-timeout-ms", VFIOPlatformDevice,
>                         mmap_timeout, 1100),
> +    DEFINE_PROP_BOOL("x-irqfd", VFIOPlatformDevice, irqfd_allowed, true),
>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> diff --git a/include/hw/vfio/vfio-platform.h b/include/hw/vfio/vfio-platform.h
> index bd1206e..097448b 100644
> --- a/include/hw/vfio/vfio-platform.h
> +++ b/include/hw/vfio/vfio-platform.h
> @@ -58,6 +58,7 @@ typedef struct VFIOPlatformDevice {
>      QEMUTimer *mmap_timer; /* enable mmaps after periods w/o interrupts */
>      start_irq_fn_t start_irq_fn;
>      QemuMutex  intp_mutex;
> +    bool irqfd_allowed; /* debug option to force irqfd on/off */
>  } VFIOPlatformDevice;
>  
>  
> diff --git a/trace-events b/trace-events
> index d3685c9..7a6a6aa 100644
> --- a/trace-events
> +++ b/trace-events
> @@ -1567,6 +1567,8 @@ vfio_platform_base_device_init(char *name, int groupid) "%s belongs to group #%d
>  vfio_platform_realize(char *name, char *compat) "vfio device %s, compat = %s"
>  vfio_intp_interrupt_set_pending(int index) "irq %d is set PENDING"
>  vfio_platform_eoi_handle_pending(int index) "handle PENDING IRQ %d"
> +vfio_platform_start_irqfd_injection(int index, int gsi, int fd, int resamplefd) "IRQ index=%d, gsi =%d, fd = %d, resamplefd = %d"
> +vfio_start_eventfd_injection(int index, int fd) "IRQ index=%d, fd = %d"
>  
>  #hw/acpi/memory_hotplug.c
>  mhp_acpi_invalid_slot_selected(uint32_t slot) "0x%"PRIx32

-- 
Alex Bennée
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