Re: [Xen-devel] Move some of the PCI device manage/control into pciback?

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 15/01/2009 10:17, "Shohei Fujiwara" <fujiwara-sxa@xxxxxxxxxxxxxxx> wrote:

> In case of HVM domain with stub domain, I'm considering direct access
> from ioemu to configuration space.  We can achieve this by mapping the
> subset of MMCFG to stub domain. This will improve the scalability of PCI
> pass-through and reduce the responsibility of dom0.
> 
> My model is the following.
> 
>     1. PCI back driver resets the device and setups it.
>     2. PCI back driver passes the responsibility of configuration
>        space of device to ioemu.
>     3. Ioemu reads/writes configuration space of the device,
>        responding guest OS.
>     4. When ioemu exits, pci back driver gets the responsibility of
>        configuration space of device.
>     5. PCI back driver resets device (and put D3hot state if possible)
> 
> As you know, current xend reads/writes configuration space. If xend
> doesn't reads/writes, the architecture becomes simpler.
> 
> What do you think about this?

I'd rather have all accesses mediated through pciback. I don't think PCI
config accesses should be on any data path anyway, and you've already taken
the hit of trapping to qemu in that case.

 -- Keir



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