Re: [Qemu-devel] [0/12] Preliminary work for IOMMU emulation support (v2)

[David Gibson]

On Fri, Oct 14, 2011 at 08:20:51PM +1100, David Gibson wrote:
> A while back, Eduard - Gabriel Munteanu send a series of patches
> implementing support for emulating the AMD IOMMU in conjunction with
> qemu emulated PCI devices.  A revised patch series added support for
> the Intel IOMMU, and I also send a revised version of this series
> which added support for the hypervisor mediated IOMMU on the pseries
> machine.
> 
> Richard Henderson also weighed in on the discussion, and there's still
> a cretain amount to be thrashed out in terms of exactly how to set up
> an IOMMU / DMA translation subsystem.
> 
> However, really only 2 or 3 patches in any of these series have
> contained anything interesting.  The rest of the series has been
> converting existing PCI emulated devices to use the new DMA interface
> which worked through the IOMMU translation, whatever it was.  While we
> keep working out what we want for the guts of the IOMMU support, these
> device conversion patches keep bitrotting against updates to the
> various device implementations themselves.
> 
> Really, regardless of whether we're actually implementing IOMMU
> translation, it makes sense that qemu code should distinguish between
> when it is really operating in CPU physical addresses and when it is
> operating in bus or DMA addresses which might have some kind of
> translation into physical addresses.
> 
> This series, therefore, begins the conversion of existing PCI device
> emulation code to use new (stub) pci dma access functions.  These are,
> for now, just defined to be untranslated cpu physical memory accesses,
> as before, but has three advantages:
> 
>    * It becomes obvious where the code is working with dma addresses,
>      so it's easier to grep for what might be affected by an IOMMU or
>      other bus address translation.
> 
>    * The new stubs take the PCIDevice *, from which any of the various
>      suggested IOMMU interfaces should be able to locate the correct
>      IOMMU translation context.
> 
>    * The new pci_dma_{read,write}() functions have a return value.
>      When we do have IOMMU support, translation failures could lead to
>      these functions failing, so we want a way to report it.
> 
> This series converts all the easy cases.  It doesn't yet handle
> devices which have both PCI and non-PCI variants, such as AHCI, OHCI
> and ne2k.  Unlike the earlier version of this series, functions using
> scatter gather _are_ covered, though.

Oh, one more note.  There are a few checkpatch failures in the series;
most are false positives (mistaking pointer * for a multiplication,
mostly).  There are a few more that are true style errors that I've
left in on the basis that matching the surrounding code is more
important than being checkpatchily correct.

-- 
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