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Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA |
Date: |
Sun, 16 Oct 2011 14:50:56 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Fri, Oct 14, 2011 at 01:14:07PM +1100, David Gibson wrote:
> On Mon, Oct 03, 2011 at 08:17:05AM -0500, Anthony Liguori wrote:
> > On 10/02/2011 07:14 AM, Michael S. Tsirkin wrote:
> > >On Sun, Oct 02, 2011 at 02:01:10PM +0200, Avi Kivity wrote:
> > >>>Hmm, not entirely virtio specific, some devices use stX macros to do the
> > >>>conversion. E.g. stw_be_phys and stl_le_phys are used in several
> > >>>places.
> > >>
> > >>These are fine - explicit endianness.
> > >
> > >Right. So changing these to e.g. stl_dma and assuming
> > >LE is default seems like a step backwards.
> >
> > We're generalizing too much.
> >
> > In general, the device model doesn't need atomic access functions.
> > That's because device model RAM access is not coherent with CPU RAM
> > access.
>
> Ok, so the next spin of these patches will have explicit LE and BE
> versions of the accessors by popular demand. I'm still using
> cpu_physical_memory_rw() as the backend though, because I can't see a
> case where a device could safely _require_ an emulated DMA access to
> be atomic.
You don't?
PCI spec supports atomic operations. It also strongly recommends
not splitting accesses below dword boundary.
> > Virtio is a very, very special case. virtio requires coherent RAM access.
>
> Right. Virtio's access to memory is *not* emulated PCI DMA, it's
> god-like hypervisor access to guest system memory. It should
> correctly bypass any IOMMU, and so should remain as
> cpu_physical_memory_rw() or the atomic accessors, rather than being
> converted to this new API.
>
> --
> David Gibson | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_
> _other_
> | _way_ _around_!
> http://www.ozlabs.org/~dgibson
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, (continued)
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, Avi Kivity, 2011/10/02
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, Michael S. Tsirkin, 2011/10/02
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, Avi Kivity, 2011/10/02
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, Anthony Liguori, 2011/10/03
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, David Gibson, 2011/10/11
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, Michael S. Tsirkin, 2011/10/12
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, David Gibson, 2011/10/13
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, Avi Kivity, 2011/10/16
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, David Gibson, 2011/10/17
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, Michael S. Tsirkin, 2011/10/18
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, Rusty Russell, 2011/10/18
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, Avi Kivity, 2011/10/19
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, David Gibson, 2011/10/19
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, David Gibson, 2011/10/11
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, Michael S. Tsirkin, 2011/10/12
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, David Gibson, 2011/10/12
- Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA, David Gibson, 2011/10/12