Re: [PATCH RFC] vhost: basic device IOTLB support

On 2015/12/31 15:13, Jason Wang wrote:

This patch tries to implement an device IOTLB for vhost. This could be
used with for co-operation with userspace(qemu) implementation of
iommu for a secure DMA environment in guest.

The idea is simple. When vhost meets an IOTLB miss, it will request
the assistance of userspace to do the translation, this is done
through:

- Fill the translation request in a preset userspace address (This
   address is set through ioctl VHOST_SET_IOTLB_REQUEST_ENTRY).
- Notify userspace through eventfd (This eventfd was set through ioctl
   VHOST_SET_IOTLB_FD).

When userspace finishes the translation, it will update the vhost
IOTLB through VHOST_UPDATE_IOTLB ioctl. Userspace is also in charge of
snooping the IOTLB invalidation of IOMMU IOTLB and use
VHOST_UPDATE_IOTLB to invalidate the possible entry in vhost.

Is there any performance data shows the difference with IOTLB 
supporting? I doubt we may see performance decrease since the flush code 
path is longer than before.

-- 
best regards
yang