linux-kernel - Re: [RFC PATCH V3 0/3] basic device IOTLB support

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Date:	Wed, 22 Jun 2016 17:53:39 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	wexu@...hat.com, peterx@...hat.com, vkaplans@...hat.com
Subject: Re: [RFC PATCH V3 0/3] basic device IOTLB support



On 2016年06月22日 00:44, Michael S. Tsirkin wrote:
> 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?
>
>

Posted, thanks.

>> 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
> --
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