Re: [PATCH v3 0/3] virtio DMA API core stuff

From	"Michael S. Tsirkin" <mst@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3 0/3] virtio DMA API core stuff
Date	2015-11-20 08:50 +0100
Message-ID	<qwOCd-4dZ-7@gated-at.bofh.it> (permalink)
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On Fri, Nov 20, 2015 at 08:56:46AM +0200, Michael S. Tsirkin wrote:
> On Thu, Nov 19, 2015 at 01:59:05PM -0800, Andy Lutomirski wrote:
> > On Nov 19, 2015 5:45 AM, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > >
> > > On Tue, Oct 27, 2015 at 11:38:57PM -0700, Andy Lutomirski wrote:
> > > > This switches virtio to use the DMA API unconditionally.  I'm sure
> > > > it breaks things, but it seems to work on x86 using virtio-pci, with
> > > > and without Xen, and using both the modern 1.0 variant and the
> > > > legacy variant.
> > >
> > > So thinking hard about it, I don't see any real drawbacks to making this
> > > conditional on a new feature bit, that Xen can then set..
> > 
> > Can you elaborate?  If I run QEMU, hosting Xen, hosting Linux, and the
> > virtio device is provided by QEMU, then how does Xen set the bit?
> 
> You would run QEMU with the appropriate flag. E.g.
> -global virtio-pci,use_platform_dma=on

Or Xen code within QEMU can tweak this global internally
so users don't need to care.

> > Similarly, how would Xen set the bit for a real physical device?
> > 
> > 
> > --Andy
> 
> There's no need to set bits for physical devices I think: from security
> point of view, using them from a VM isn't very different from using them
> from host.
> 
> 
> 
> -- 
> MST
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Re: [PATCH v3 0/3] virtio DMA API core stuff "Michael S. Tsirkin" <mst@redhat.com> - 2015-11-19 14:50 +0100
  Re: [PATCH v3 0/3] virtio DMA API core stuff Andy Lutomirski <luto@amacapital.net> - 2015-11-19 23:00 +0100
    Re: [PATCH v3 0/3] virtio DMA API core stuff David Woodhouse <dwmw2@infradead.org> - 2015-11-20 00:40 +0100
      Re: [PATCH v3 0/3] virtio DMA API core stuff Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2015-11-20 04:00 +0100
        Re: [PATCH v3 0/3] virtio DMA API core stuff "Michael S. Tsirkin" <mst@redhat.com> - 2015-11-20 09:40 +0100
      Re: [PATCH v3 0/3] virtio DMA API core stuff "Michael S. Tsirkin" <mst@redhat.com> - 2015-11-20 09:30 +0100
        Re: [PATCH v3 0/3] virtio DMA API core stuff David Woodhouse <dwmw2@infradead.org> - 2015-11-22 17:00 +0100
          Re: [PATCH v3 0/3] virtio DMA API core stuff "Michael S. Tsirkin" <mst@redhat.com> - 2015-11-22 23:00 +0100
            Re: [PATCH v3 0/3] virtio DMA API core stuff "David Woodhouse" <dwmw2@infradead.org> - 2015-11-23 00:10 +0100
              Re: [PATCH v3 0/3] virtio DMA API core stuff "Michael S. Tsirkin" <mst@redhat.com> - 2015-11-23 09:00 +0100
            Re: [PATCH v3 0/3] virtio DMA API core stuff "David Woodhouse" <dwmw2@infradead.org> - 2015-11-23 00:10 +0100
    Re: [PATCH v3 0/3] virtio DMA API core stuff "Michael S. Tsirkin" <mst@redhat.com> - 2015-11-20 08:00 +0100
      Re: [PATCH v3 0/3] virtio DMA API core stuff "Michael S. Tsirkin" <mst@redhat.com> - 2015-11-20 08:50 +0100

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