netdev - Re: [PATCH 3/5] vDPA: introduce vDPA bus

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200121004047-mutt-send-email-mst@kernel.org>
Date:   Tue, 21 Jan 2020 00:47:15 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Jason Gunthorpe <jgg@...lanox.com>,
        Shahaf Shuler <shahafs@...lanox.com>,
        Rob Miller <rob.miller@...adcom.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        Netdev <netdev@...r.kernel.org>,
        "Bie, Tiwei" <tiwei.bie@...el.com>,
        "maxime.coquelin@...hat.com" <maxime.coquelin@...hat.com>,
        "Liang, Cunming" <cunming.liang@...el.com>,
        "Wang, Zhihong" <zhihong.wang@...el.com>,
        "Wang, Xiao W" <xiao.w.wang@...el.com>,
        "haotian.wang@...ive.com" <haotian.wang@...ive.com>,
        "Zhu, Lingshan" <lingshan.zhu@...el.com>,
        "eperezma@...hat.com" <eperezma@...hat.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        Parav Pandit <parav@...lanox.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "stefanha@...hat.com" <stefanha@...hat.com>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "hch@...radead.org" <hch@...radead.org>,
        Ariel Adam <aadam@...hat.com>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        Jiri Pirko <jiri@...lanox.com>,
        "hanand@...inx.com" <hanand@...inx.com>,
        "mhabets@...arflare.com" <mhabets@...arflare.com>
Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus

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

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
> 


-- 
MST