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[Xen-ia64-devel] Re: [Xen-devel] [PATCH][RFC] 3/3 Fix [ia64] PV driver domains - ugly python hacks

On Thu, Aug 07, 2008 at 02:20:34PM -0600, Alex Williamson wrote:
> x86 IOMMU support added a lot of assumptions about what PCI buses look
> like and where to find bridge devices.  On ia64, we don't yet have
> virtualization friendly IOMMUs, so for the moment, we just want to keep
> "unsafe" PV PCI pass through working as well as it did in Xen 3.2.
> Looking at the code, it almost seems like x86 has thrown out support for
> the old style driver domain.  Things that don't necessarily work on
> every PCI compliant architecture:
>       * You can't assume that just because there's a device at 01:01.0
>         that there's also a bridge at 01:00.0 and blow-up when you don't
>         find it.???  On HP ia64 boxes, PCI root bridges are not
>         necessarily exposed as a PCI device.  This pretty much means we
>         can't call into any of the "FLR" code paths.
>       * BAR alignment: it's hard to have BAR alignment when your page
>         size is 16k.  This wasn't a requirement for previous PV driver
>         domains, so I assume it's only for IOMMU support.
> This is ugly, so I'm open to suggestions.  It seems that all of these
> architecture checks could be replaced by checking some "iommu_present"
> variable to test whether the extra requirements are necessary.
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxx>

Given that iommu is disabled on x86 by default,
this functional regression is accidental, I guess.
I think a sort of this patch is necessary for the next release.
(at least for IA64)


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