Re: [Qemu-devel] [PATCH 0/2] intel_iommu: Add support for translation for devices behind bridges

[Knut Omang]

On Tue, 2014-10-21 at 01:29 +0200, Alexander Graf wrote:
> 
> 
> > Am 21.10.2014 um 00:34 schrieb Knut Omang <address@hidden>:
> > 
> > This patch set changes the data structure used to handle address spaces 
> > within
> > the emulated Intel iommu to support traversal also if bus numbers are 
> > dynamically
> > allocated, as is the case for devices that sit behind root ports or 
> > downstream switches.
> > This means that we cannot use bus number as index, instead a QLIST is used.
> > 
> > This requires a change in the API for setup of IOMMUs which is taken care 
> > of by 
> > the first patch. The second patch implements the fix.
> 
> Are you sure that this works on real hardware? How does that one
> communicate sub-bridge liodns to the iommu? How do they get indexed
> from software?

I do not claim to fully understand the details of how this is
implemented in hardware, but I believe the implementation I propose here
should be functionally equivalent to what the Intel IOMMU offers, and
similar to the original implementation here, except that the data
structure is valid also before enumeration when behind buses.

After enumeration, the only difference would be that during
invalidation, there is a list search for the right bus rather than an
index lookup as before, slightly less efficient but at the benefit of
being independent of bus numbering during setup.

Wrt the currently implemented IOMMUs for other architectures, they were
all ignoring the bus argument anyway, so the API change did not make
much difference.

Knut

> Alex
>