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Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api

From "Michael S. Tsirkin" <mst@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api
Date 2016-04-27 20:20 +0200
Message-ID <rsCe7-5LS-25@gated-at.bofh.it> (permalink)
References (4 earlier) <rsyDw-2GX-31@gated-at.bofh.it> <rsyNc-2L2-21@gated-at.bofh.it> <rsz6z-2T0-19@gated-at.bofh.it> <rszge-3gp-11@gated-at.bofh.it> <rszpV-3jV-29@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Wed, Apr 27, 2016 at 04:15:35PM +0100, David Woodhouse wrote:
> On Wed, 2016-04-27 at 18:05 +0300, Michael S. Tsirkin wrote:
> > 
> > I really don't get it.
> > 
> > There's exactly one device that works now and needs the work-around and
> > so that we need to support, and that is virtio. It happens to have
> > exactly the same issue on all platforms.
> 
> False. We have other devices which are currently *not* translated by
> the emulated IOMMU and which aren't going to be in the short term
> either.
> 
> We also have other devices (emulated hardware NICs) to which precisely
> the same "we don't need protection" arguments apply, and which we
> *could* expose to the guest without an IOMMU translation if we really
> wanted to. It makes as much sense as exposing virtio without an IOMMU,
> going forward.

The reasons for virtio are mostly dealing legacy.
We don't need protection is a separate issue
that I'd rather drop for now.

> > Why would we want to work hard to build platform-specific
> > solutions to a problem that can be solved in 5 lines of
> > generic code?
> 
> Because it's a dirty hack in the *wrong* place.

No one came up with a better one so far :(

> -- 
> dwmw2

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Thread

[PATCH V2 RFC] fixup! virtio: convert to use DMA api "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-21 15:50 +0200
  Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Wei Liu <wei.liu2@citrix.com> - 2016-04-21 16:00 +0200
    Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api David Woodhouse <dwmw2@infradead.org> - 2016-04-27 14:20 +0200
      Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-27 15:40 +0200
        Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Joerg Roedel <joro@8bytes.org> - 2016-04-27 16:30 +0200
          Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-27 16:40 +0200
            Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Joerg Roedel <joro@8bytes.org> - 2016-04-27 17:00 +0200
              Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-27 17:10 +0200
                Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api David Woodhouse <dwmw2@infradead.org> - 2016-04-27 17:20 +0200
                Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-27 20:20 +0200
                Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api David Woodhouse <dwmw2@infradead.org> - 2016-04-27 21:20 +0200
          Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-27 16:40 +0200
            Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Andy Lutomirski <luto@amacapital.net> - 2016-04-27 16:50 +0200
              Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-27 17:00 +0200
                Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Joerg Roedel <joro@8bytes.org> - 2016-04-27 17:00 +0200
                Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-27 17:10 +0200
                Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Andy Lutomirski <luto@amacapital.net> - 2016-04-27 17:20 +0200
          Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Andy Lutomirski <luto@amacapital.net> - 2016-04-27 16:40 +0200
  Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Stefan Hajnoczi <stefanha@redhat.com> - 2016-04-21 17:00 +0200
    Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api "Michael S. Tsirkin" <mst@redhat.com> - 2016-04-21 17:20 +0200
      Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api Stefan Hajnoczi <stefanha@gmail.com> - 2016-04-22 11:40 +0200

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