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SubjectRe: [PATCH v2 1/5] virtio-mmio: add notify feature for per-queue
On Mon, Feb 10, 2020 at 05:05:17PM +0800, Zha Bin wrote:
> From: Liu Jiang <gerry@linux.alibaba.com>
>
> The standard virtio-mmio devices use notification register to signal
> backend. This will cause vmexits and slow down the performance when we
> passthrough the virtio-mmio devices to guest virtual machines.
> We proposed to update virtio over MMIO spec to add the per-queue
> notify feature VIRTIO_F_MMIO_NOTIFICATION[1]. It can allow the VMM to
> configure notify location for each queue.
>
> [1] https://lkml.org/lkml/2020/1/21/31
>
> Signed-off-by: Liu Jiang <gerry@linux.alibaba.com>
> Co-developed-by: Zha Bin <zhabin@linux.alibaba.com>
> Signed-off-by: Zha Bin <zhabin@linux.alibaba.com>
> Co-developed-by: Jing Liu <jing2.liu@linux.intel.com>
> Signed-off-by: Jing Liu <jing2.liu@linux.intel.com>
> Co-developed-by: Chao Peng <chao.p.peng@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>

So this is for pass-through for nested virt?
OK but let's split this out please, and benchmark separately.


> ---
> drivers/virtio/virtio_mmio.c | 37 +++++++++++++++++++++++++++++++++++--
> include/uapi/linux/virtio_config.h | 8 +++++++-
> 2 files changed, 42 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
> index 97d5725..1733ab97 100644
> --- a/drivers/virtio/virtio_mmio.c
> +++ b/drivers/virtio/virtio_mmio.c
> @@ -90,6 +90,9 @@ struct virtio_mmio_device {
> /* a list of queues so we can dispatch IRQs */
> spinlock_t lock;
> struct list_head virtqueues;
> +
> + unsigned short notify_base;
> + unsigned short notify_multiplier;
> };
>
> struct virtio_mmio_vq_info {
> @@ -98,6 +101,9 @@ struct virtio_mmio_vq_info {
>
> /* the list node for the virtqueues list */
> struct list_head node;
> +
> + /* Notify Address*/
> + unsigned int notify_addr;
> };
>
>
> @@ -119,13 +125,23 @@ static u64 vm_get_features(struct virtio_device *vdev)
> return features;
> }
>
> +static void vm_transport_features(struct virtio_device *vdev, u64 features)
> +{
> + if (features & BIT_ULL(VIRTIO_F_MMIO_NOTIFICATION))
> + __virtio_set_bit(vdev, VIRTIO_F_MMIO_NOTIFICATION);
> +}
> +
> static int vm_finalize_features(struct virtio_device *vdev)
> {
> struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
> + u64 features = vdev->features;
>
> /* Give virtio_ring a chance to accept features. */
> vring_transport_features(vdev);
>
> + /* Give virtio_mmio a chance to accept features. */
> + vm_transport_features(vdev, features);
> +
> /* Make sure there is are no mixed devices */
> if (vm_dev->version == 2 &&
> !__virtio_test_bit(vdev, VIRTIO_F_VERSION_1)) {
> @@ -272,10 +288,13 @@ static void vm_reset(struct virtio_device *vdev)
> static bool vm_notify(struct virtqueue *vq)
> {
> struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vq->vdev);
> + struct virtio_mmio_vq_info *info = vq->priv;
>
> - /* We write the queue's selector into the notification register to
> + /* We write the queue's selector into the Notify Address to
> * signal the other end */
> - writel(vq->index, vm_dev->base + VIRTIO_MMIO_QUEUE_NOTIFY);
> + if (info)
> + writel(vq->index, vm_dev->base + info->notify_addr);
> +
> return true;
> }
>
> @@ -434,6 +453,12 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned index,
> vq->priv = info;
> info->vq = vq;
>
> + if (__virtio_test_bit(vdev, VIRTIO_F_MMIO_NOTIFICATION))
> + info->notify_addr = vm_dev->notify_base +
> + vm_dev->notify_multiplier * vq->index;
> + else
> + info->notify_addr = VIRTIO_MMIO_QUEUE_NOTIFY;
> +
> spin_lock_irqsave(&vm_dev->lock, flags);
> list_add(&info->node, &vm_dev->virtqueues);
> spin_unlock_irqrestore(&vm_dev->lock, flags);
> @@ -471,6 +496,14 @@ static int vm_find_vqs(struct virtio_device *vdev, unsigned nvqs,
> return irq;
> }
>
> + if (__virtio_test_bit(vdev, VIRTIO_F_MMIO_NOTIFICATION)) {
> + unsigned int notify = readl(vm_dev->base +
> + VIRTIO_MMIO_QUEUE_NOTIFY);
> +
> + vm_dev->notify_base = notify & 0xffff;
> + vm_dev->notify_multiplier = (notify >> 16) & 0xffff;
> + }
> +
> err = request_irq(irq, vm_interrupt, IRQF_SHARED,
> dev_name(&vdev->dev), vm_dev);
> if (err)
> diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
> index ff8e7dc..5d93c01 100644
> --- a/include/uapi/linux/virtio_config.h
> +++ b/include/uapi/linux/virtio_config.h
> @@ -52,7 +52,7 @@
> * rest are per-device feature bits.
> */
> #define VIRTIO_TRANSPORT_F_START 28
> -#define VIRTIO_TRANSPORT_F_END 38
> +#define VIRTIO_TRANSPORT_F_END 40
>
> #ifndef VIRTIO_CONFIG_NO_LEGACY
> /* Do we get callbacks when the ring is completely used, even if we've
> @@ -88,4 +88,10 @@
> * Does the device support Single Root I/O Virtualization?
> */
> #define VIRTIO_F_SR_IOV 37
> +
> +/*
> + * This feature indicates the enhanced notification support on MMIO transport
> + * layer.
> + */
> +#define VIRTIO_F_MMIO_NOTIFICATION 39
> #endif /* _UAPI_LINUX_VIRTIO_CONFIG_H */
> --
> 1.8.3.1

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