Subject: Re: [RFC PATCH V3 0/3] basic device IOTLB support

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 21 Jun 2016 19:44:49 +0300

On Tue, May 24, 2016 at 05:36:22PM +0800, Jason Wang wrote:
> This patch tries to implement an device IOTLB for vhost. This could be
> used with for co-operation with userspace IOMMU implementation (qemu)
> for a secure DMA environment (DMAR) 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:
> 
> - when there's a IOTLB miss, it will notify userspace through
>   vhost_net fd and then userspace read the fault address, size and
>   access from vhost fd.
> - userspace write the translation result back to vhost fd, vhost can
>   then update its IOTLB.
> 
> The codes were optimized for fixed mapping users e.g dpdk in guest. It
> will be slow if dynamic mappings were used in guest. We could do
> optimizations on top.
> 
> The codes were designed to be architecture independent. It should be
> easily ported to any architecture.
> 
> Stress tested with l2fwd/vfio in guest with 4K/2M/1G page size. On 1G
> hugepage case, 100% TLB hit rate were noticed.
> 
> Changes from V2:
> - introduce memory accessors for vhost
> - switch from ioctls to oridinary file read/write for iotlb miss and
>   updating
> - do not assume virtqueue were virtually mapped contiguously, all
>   virtqueue access were done throug IOTLB
> - verify memory access during IOTLB update and fail early
> - introduce a module parameter for the size of IOTLB
> 
> Changes from V1:
> - support any size/range of updating and invalidation through
>   introducing the interval tree.
> - convert from per device iotlb request to per virtqueue iotlb
>   request, this solves the possible deadlock in V1.
> - read/write permission check support.
> 
> Please review.

Nice, this looks good to me. Can you post a non-rfc please?

> Jason Wang (3):
>   vhost: introduce vhost memory accessors
>   vhost: convert pre sorted vhost memory array to interval tree
>   vhost: device IOTLB API
> 
>  drivers/vhost/net.c        |  63 +++-
>  drivers/vhost/vhost.c      | 760 ++++++++++++++++++++++++++++++++++++++-------
>  drivers/vhost/vhost.h      |  60 +++-
>  include/uapi/linux/vhost.h |  28 ++
>  4 files changed, 790 insertions(+), 121 deletions(-)
> 
> -- 
> 2.7.4