On Thu, Nov 19, 2015 at 12:50:49PM +0300, Pavel Fedin wrote:
> If you happen to have a kernel with ioeventfd support enabled, but
> missing support for them in KVM, and you attempt to enable vhost by
> setting vhost=on, qemu aborts with error:
>
> kvm_mem_ioeventfd_add: error adding ioeventfd: Function not implemented
>
> This patch adds a mechanism which allows to emulate KVM binding by
> triggering the related notifiers via the userspace. The first time the
> emulation is used, a warning is displayed, so that the user knows about
> potential performance impact:
>
> 2015-11-19T09:35:16.618380Z qemu-system-aarch64: KVM does not support eventfd
> binding, using userspace event forwarding (slow)
>
> This problem can be observed with libvirt, which checks for /dev/vhost-net
> availability and just inserts "vhost=on" automatically in this case; on an
> ARM64 system using stock kernel 3.18.0 with CONFIG_IOEVENTFD enabled in
> expert settings.
>
> Signed-off-by: Pavel Fedin <p.fe...@samsung.com>
OK, that's better, thanks!
Why do we need
if (kvm_eventfds_enabled()) {
memory_region_add_eventfd(&proxy->iomem, VIRTIO_MMIO_QUEUENOTIFY, 4,
true, n, notifier);
} else if (!set_handler) {
virtio_queue_set_host_notifier_forwarding(vq);
}
everywhere though?
Can't memory_region_add_eventfd DTRT depending on kvm etc?
> ---
> hw/virtio/virtio-mmio.c | 15 +++++++++---
> hw/virtio/virtio-pci.c | 61
> ++++++++++++++++++++++++++--------------------
> hw/virtio/virtio.c | 24 +++++++++++++++++-
> include/hw/virtio/virtio.h | 1 +
> 4 files changed, 69 insertions(+), 32 deletions(-)
>
> diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c
> index 16621fa..69d4cbc 100644
> --- a/hw/virtio/virtio-mmio.c
> +++ b/hw/virtio/virtio-mmio.c
> @@ -110,11 +110,18 @@ static int
> virtio_mmio_set_host_notifier_internal(VirtIOMMIOProxy *proxy,
> return r;
> }
> virtio_queue_set_host_notifier_fd_handler(vq, true, set_handler);
> - memory_region_add_eventfd(&proxy->iomem, VIRTIO_MMIO_QUEUENOTIFY, 4,
> - true, n, notifier);
> +
> + if (kvm_eventfds_enabled()) {
> + memory_region_add_eventfd(&proxy->iomem,
> VIRTIO_MMIO_QUEUENOTIFY, 4,
> + true, n, notifier);
> + } else if (!set_handler) {
> + virtio_queue_set_host_notifier_forwarding(vq);
> + }
> } else {
> - memory_region_del_eventfd(&proxy->iomem, VIRTIO_MMIO_QUEUENOTIFY, 4,
> - true, n, notifier);
> + if (kvm_eventfds_enabled()) {
> + memory_region_del_eventfd(&proxy->iomem,
> VIRTIO_MMIO_QUEUENOTIFY, 4,
> + true, n, notifier);
> + }
> virtio_queue_set_host_notifier_fd_handler(vq, false, false);
> event_notifier_cleanup(notifier);
> }
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 96be4fd..b27a630 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -293,41 +293,48 @@ static int
> virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
> return r;
> }
> virtio_queue_set_host_notifier_fd_handler(vq, true, set_handler);
> - if (modern) {
> - if (fast_mmio) {
> - memory_region_add_eventfd(modern_mr, modern_addr, 0,
> - false, n, notifier);
> - } else {
> - memory_region_add_eventfd(modern_mr, modern_addr, 2,
> - false, n, notifier);
> +
> + if (kvm_eventfds_enabled()) {
> + if (modern) {
> + if (fast_mmio) {
> + memory_region_add_eventfd(modern_mr, modern_addr, 0,
> + false, n, notifier);
> + } else {
> + memory_region_add_eventfd(modern_mr, modern_addr, 2,
> + false, n, notifier);
> + }
> + if (modern_pio) {
> + memory_region_add_eventfd(modern_notify_mr, 0, 2,
> + true, n, notifier);
> + }
> }
> - if (modern_pio) {
> - memory_region_add_eventfd(modern_notify_mr, 0, 2,
> - true, n, notifier);
> + if (legacy) {
> + memory_region_add_eventfd(legacy_mr, legacy_addr, 2,
> + true, n, notifier);
> }
> - }
> - if (legacy) {
> - memory_region_add_eventfd(legacy_mr, legacy_addr, 2,
> - true, n, notifier);
> + } else if (!set_handler) {
> + virtio_queue_set_host_notifier_forwarding(vq);
> }
> } else {
> - if (modern) {
> - if (fast_mmio) {
> - memory_region_del_eventfd(modern_mr, modern_addr, 0,
> - false, n, notifier);
> - } else {
> - memory_region_del_eventfd(modern_mr, modern_addr, 2,
> - false, n, notifier);
> + if (kvm_eventfds_enabled()) {
> + if (modern) {
> + if (fast_mmio) {
> + memory_region_del_eventfd(modern_mr, modern_addr, 0,
> + false, n, notifier);
> + } else {
> + memory_region_del_eventfd(modern_mr, modern_addr, 2,
> + false, n, notifier);
> + }
> + if (modern_pio) {
> + memory_region_del_eventfd(modern_notify_mr, 0, 2,
> + true, n, notifier);
> + }
> }
> - if (modern_pio) {
> - memory_region_del_eventfd(modern_notify_mr, 0, 2,
> + if (legacy) {
> + memory_region_del_eventfd(legacy_mr, legacy_addr, 2,
> true, n, notifier);
> }
> }
> - if (legacy) {
> - memory_region_del_eventfd(legacy_mr, legacy_addr, 2,
> - true, n, notifier);
> - }
> virtio_queue_set_host_notifier_fd_handler(vq, false, false);
> event_notifier_cleanup(notifier);
> }
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 1edef59..6fe268f 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -89,6 +89,7 @@ struct VirtQueue
> VirtIODevice *vdev;
> EventNotifier guest_notifier;
> EventNotifier host_notifier;
> + bool forward_host_notifier;
> QLIST_ENTRY(VirtQueue) node;
> };
>
> @@ -969,7 +970,13 @@ void virtio_queue_notify_vq(VirtQueue *vq)
>
> void virtio_queue_notify(VirtIODevice *vdev, int n)
> {
> - virtio_queue_notify_vq(&vdev->vq[n]);
> + VirtQueue *vq = &vdev->vq[n];
> +
> + if (vq->forward_host_notifier) {
> + event_notifier_set(&vq->host_notifier);
> + } else {
> + virtio_queue_notify_vq(&vdev->vq[n]);
> + }
> }
>
> uint16_t virtio_queue_vector(VirtIODevice *vdev, int n)
> @@ -1715,6 +1722,21 @@ void
> virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
> /* Test and clear notifier before after disabling event,
> * in case poll callback didn't have time to run. */
> virtio_queue_host_notifier_read(&vq->host_notifier);
> +
> + vq->forward_host_notifier = false;
> + }
> +}
> +
> +static bool forwarding_warning;
> +
> +void virtio_queue_set_host_notifier_forwarding(VirtQueue *vq)
> +{
> + vq->forward_host_notifier = true;
> +
> + if (!forwarding_warning) {
> + forwarding_warning = true;
> + error_report("KVM does not support eventfd binding, "
> + "using userspace event forwarding (slow)");
> }
> }
>
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index 205fadf..f288ccb 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -245,6 +245,7 @@ void virtio_queue_set_guest_notifier_fd_handler(VirtQueue
> *vq, bool assign,
> EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq);
> void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
> bool set_handler);
> +void virtio_queue_set_host_notifier_forwarding(VirtQueue *vq);
> void virtio_queue_notify_vq(VirtQueue *vq);
> void virtio_irq(VirtQueue *vq);
> VirtQueue *virtio_vector_first_queue(VirtIODevice *vdev, uint16_t vector);
> --
> 1.9.5.msysgit.0
>
