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From: Shahaf Shuler <shahafs@mellanox.com>
To: Jason Wang <jasowang@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Gunthorpe <jgg@mellanox.com>,
	Rob Miller <rob.miller@broadcom.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>,
	Netdev <netdev@vger.kernel.org>,
	"Bie, Tiwei" <tiwei.bie@intel.com>,
	"maxime.coquelin@redhat.com" <maxime.coquelin@redhat.com>,
	"Liang, Cunming" <cunming.liang@intel.com>,
	"Wang, Zhihong" <zhihong.wang@intel.com>,
	"Wang, Xiao W" <xiao.w.wang@intel.com>,
	"haotian.wang@sifive.com" <haotian.wang@sifive.com>,
	"Zhu, Lingshan" <lingshan.zhu@intel.com>,
	"eperezma@redhat.com" <eperezma@redhat.com>,
	"lulu@redhat.com" <lulu@redhat.com>,
	Parav Pandit <parav@mellanox.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	"stefanha@redhat.com" <stefanha@redhat.com>,
	"rdunlap@infradead.org" <rdunlap@infradead.org>,
	"hch@infradead.org" <hch@infradead.org>,
	Ariel Adam <aadam@redhat.com>, Jiri Pirko <jiri@mellanox.com>,
	"hanand@xilinx.com" <hanand@xilinx.com>,
	"mhabets@solarflare.com" <mhabets@solarflare.com>
Subject: RE: [PATCH 3/5] vDPA: introduce vDPA bus
Date: Tue, 21 Jan 2020 11:09:38 +0000
Message-ID: <AM0PR0502MB37956A8D6690B190EEA713A5C30D0@AM0PR0502MB3795.eurprd05.prod.outlook.com> (raw)
In-Reply-To: <028ed448-a948-79d9-f224-c325029b17ab@redhat.com>

Tuesday, January 21, 2020 10:35 AM, Jason Wang:
> Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus
> 
> 
> On 2020/1/21 下午4:15, Michael S. Tsirkin wrote:
> > On Tue, Jan 21, 2020 at 04:00:38PM +0800, Jason Wang wrote:
> >> On 2020/1/21 下午1:47, Michael S. Tsirkin wrote:
> >>> On Tue, Jan 21, 2020 at 12:00:57PM +0800, Jason Wang wrote:
> >>>> On 2020/1/21 上午1:49, Jason Gunthorpe wrote:
> >>>>> On Mon, Jan 20, 2020 at 04:43:53PM +0800, Jason Wang wrote:
> >>>>>> This is similar to the design of platform IOMMU part of
> >>>>>> vhost-vdpa. We decide to send diffs to platform IOMMU there. If
> >>>>>> it's ok to do that in driver, we can replace set_map with incremental
> API like map()/unmap().
> >>>>>>
> >>>>>> Then driver need to maintain rbtree itself.
> >>>>> I think we really need to see two modes, one where there is a
> >>>>> fixed translation without dynamic vIOMMU driven changes and one
> >>>>> that supports vIOMMU.
> >>>> I think in this case, you meant the method proposed by Shahaf that
> >>>> sends diffs of "fixed translation" to device?
> >>>>
> >>>> It would be kind of tricky to deal with the following case for example:
> >>>>
> >>>> old map [4G, 16G) new map [4G, 8G)
> >>>>
> >>>> If we do
> >>>>
> >>>> 1) flush [4G, 16G)
> >>>> 2) add [4G, 8G)
> >>>>
> >>>> There could be a window between 1) and 2).
> >>>>
> >>>> It requires the IOMMU that can do
> >>>>
> >>>> 1) remove [8G, 16G)
> >>>> 2) flush [8G, 16G)
> >>>> 3) change [4G, 8G)
> >>>>
> >>>> ....
> >>> Basically what I had in mind is something like qemu memory api
> >>>
> >>> 0. begin
> >>> 1. remove [8G, 16G)
> >>> 2. add [4G, 8G)
> >>> 3. commit
> >>
> >> This sounds more flexible e.g driver may choose to implement static
> >> mapping one through commit. But a question here, it looks to me this
> >> still requires the DMA to be synced with at least commit here.
> >> Otherwise device may get DMA fault? Or device is expected to be paused
> DMA during begin?
> >>
> >> Thanks
> > For example, commit might switch one set of tables for another,
> > without need to pause DMA.
> 
> 
> Yes, I think that works but need confirmation from Shahaf or Jason.

From my side, as I wrote, I would like to see the suggested function prototype along w/ the definition of the expectation from driver upon calling those. 
It is not 100% clear to me what should be the outcome of remove/flush/change/commit

> 
> Thanks
> 
> 
> 
> >
> >>> Anyway, I'm fine with a one-shot API for now, we can improve it
> >>> later.
> >>>
> >>>>> There are different optimization goals in the drivers for these
> >>>>> two configurations.
> >>>>>
> >>>>>>> If the first one, then I think memory hotplug is a heavy flow
> >>>>>>> regardless. Do you think the extra cycles for the tree traverse
> >>>>>>> will be visible in any way?
> >>>>>> I think if the driver can pause the DMA during the time for
> >>>>>> setting up new mapping, it should be fine.
> >>>>> This is very tricky for any driver if the mapping change hits the
> >>>>> virtio rings. :(
> >>>>>
> >>>>> Even a IOMMU using driver is going to have problems with that..
> >>>>>
> >>>>> Jason
> >>>> Or I wonder whether ATS/PRI can help here. E.g during I/O page
> >>>> fault, driver/device can wait for the new mapping to be set and
> >>>> then replay the DMA.
> >>>>
> >>>> Thanks
> >>>>


  reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16 12:42 [PATCH 0/5] vDPA support Jason Wang
2020-01-16 12:42 ` [PATCH 1/5] vhost: factor out IOTLB Jason Wang
2020-01-17  4:14   ` Randy Dunlap
2020-01-17  9:34     ` Jason Wang
2020-01-18  0:01   ` kbuild test robot
2020-01-18  0:40   ` kbuild test robot
2020-01-16 12:42 ` [PATCH 2/5] vringh: IOTLB support Jason Wang
2020-01-17 21:54   ` kbuild test robot
2020-01-17 22:33   ` kbuild test robot
2020-01-16 12:42 ` [PATCH 3/5] vDPA: introduce vDPA bus Jason Wang
2020-01-16 15:22   ` Jason Gunthorpe
2020-01-17  3:03     ` Jason Wang
2020-01-17 13:54       ` Jason Gunthorpe
2020-01-20  7:50         ` Jason Wang
2020-01-20 12:17         ` Michael S. Tsirkin
2020-01-20 17:50           ` Jason Gunthorpe
2020-01-20 21:56             ` Michael S. Tsirkin
2020-01-21 14:12               ` Jason Gunthorpe
2020-01-21 14:15                 ` Michael S. Tsirkin
2020-01-21 14:16                   ` Jason Gunthorpe
2020-01-21  8:40       ` Tian, Kevin
2020-01-21  9:41         ` Jason Wang
2020-01-17  4:16   ` Randy Dunlap
2020-01-17  9:34     ` Jason Wang
2020-01-17 12:13   ` Michael S. Tsirkin
2020-01-17 13:52     ` Jason Wang
     [not found]       ` <CAJPjb1+fG9L3=iKbV4Vn13VwaeDZZdcfBPvarogF_Nzhk+FnKg@mail.gmail.com>
2020-01-19  9:07         ` Shahaf Shuler
2020-01-19  9:59           ` Michael S. Tsirkin
2020-01-20  8:44             ` Jason Wang
2020-01-20 12:09               ` Michael S. Tsirkin
2020-01-21  3:32                 ` Jason Wang
2020-01-20  8:43           ` Jason Wang
2020-01-20 17:49             ` Jason Gunthorpe
2020-01-20 20:51               ` Shahaf Shuler
2020-01-20 21:25                 ` Michael S. Tsirkin
2020-01-20 21:47                   ` Shahaf Shuler
2020-01-20 21:59                     ` Michael S. Tsirkin
2020-01-21  6:01                       ` Shahaf Shuler
2020-01-21  7:57                         ` Jason Wang
2020-01-21 14:07                   ` Jason Gunthorpe
2020-01-21 14:16                     ` Michael S. Tsirkin
2020-01-20 21:48               ` Michael S. Tsirkin
2020-01-21  4:00               ` Jason Wang
2020-01-21  5:47                 ` Michael S. Tsirkin
2020-01-21  8:00                   ` Jason Wang
2020-01-21  8:15                     ` Michael S. Tsirkin
2020-01-21  8:35                       ` Jason Wang
2020-01-21 11:09                         ` Shahaf Shuler [this message]
2020-01-22  6:36                           ` Jason Wang
2020-01-21 14:05                       ` Jason Gunthorpe
2020-01-21 14:17                         ` Michael S. Tsirkin
2020-01-22  6:18                           ` Jason Wang
2020-01-20  8:19         ` Jason Wang
2020-01-16 12:42 ` [PATCH 4/5] virtio: introduce a vDPA based transport Jason Wang
2020-01-16 15:38   ` Jason Gunthorpe
2020-01-17  9:32     ` Jason Wang
2020-01-17 14:00       ` Jason Gunthorpe
2020-01-20  7:52         ` Jason Wang
2020-01-17  4:10   ` Randy Dunlap
2020-01-16 12:42 ` [PATCH 5/5] vdpasim: vDPA device simulator Jason Wang
2020-01-16 15:47   ` Jason Gunthorpe
2020-01-17  9:32     ` Jason Wang
2020-01-17 14:10       ` Jason Gunthorpe
2020-01-20  8:01         ` Jason Wang
2020-02-04  4:19         ` Jason Wang
2020-01-17  4:12   ` Randy Dunlap
2020-01-17  9:35     ` Jason Wang
2020-01-18 18:18   ` kbuild test robot
2020-01-28  3:32   ` Dan Carpenter
2020-02-04  4:07     ` Jason Wang
2020-02-04  8:21   ` Zhu Lingshan
2020-02-04  8:28     ` Jason Wang
2020-02-04 12:52       ` Jason Gunthorpe
2020-02-05  3:14         ` Jason Wang
2020-01-21  8:44 ` [PATCH 0/5] vDPA support Tian, Kevin
2020-01-21  9:39   ` Jason Wang

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