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Subject[PATCH v2 1/5] virtio-mmio: add notify feature for per-queue
Date
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>
---
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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