From: Liu Jiang <ge...@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 <ge...@linux.alibaba.com> Co-developed-by: Zha Bin <zha...@linux.alibaba.com> Signed-off-by: Zha Bin <zha...@linux.alibaba.com> Co-developed-by: Jing Liu <jing2....@linux.intel.com> Signed-off-by: Jing Liu <jing2....@linux.intel.com> Co-developed-by: Chao Peng <chao.p.p...@linux.intel.com> Signed-off-by: Chao Peng <chao.p.p...@linux.intel.com> --- 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