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virtio: support VIRTIO_F_ORDER_PLATFORM

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This patch introduces the support for VIRTIO_F_ORDER_PLATFORM.
If this feature is negotiated, the driver must use the barriers
suitable for hardware devices. Otherwise, the device and driver
are assumed to be implemented in software, that is they can be
assumed to run on identical CPUs in an SMP configuration. Thus
a weaker form of memory barriers is sufficient to yield better
performance.

It is recommended that an add-in card based PCI device offers
this feature for portability. The device will fail to operate
further or will operate in a slower emulation mode if this
feature is offered but not accepted.

Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Tiwei Bie
2019-01-23 17:50:26 +08:00
committed by Michael S. Tsirkin
parent 49a57857ae
commit 45383fb0f4
2 changed files with 14 additions and 0 deletions
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8
drivers/virtio/virtio_ring.c
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@@ -1609,6 +1609,9 @@ static struct virtqueue *vring_create_virtqueue_packed(
!context;
vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
vq->weak_barriers = false;
vq->packed.ring_dma_addr = ring_dma_addr;
vq->packed.driver_event_dma_addr = driver_event_dma_addr;
vq->packed.device_event_dma_addr = device_event_dma_addr;
@@ -2079,6 +2082,9 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
!context;
vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
vq->weak_barriers = false;
vq->split.queue_dma_addr = 0;
vq->split.queue_size_in_bytes = 0;
@@ -2213,6 +2219,8 @@ void vring_transport_features(struct virtio_device *vdev)
break;
case VIRTIO_F_RING_PACKED:
break;
case VIRTIO_F_ORDER_PLATFORM:
break;
default:
/* We don't understand this bit. */
__virtio_clear_bit(vdev, i);