Re: [GIT PULL] Intel IOMMU for 4.1

[David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>]

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On Mon, 2015-04-27 at 09:39 -0600, Alex Williamson wrote:
> David,
> 
> Since this got pulled anyway, do you plan to follow-up with patches to
> limit the graphics RMRR exception to the known and acceptable uses and
> document them, or should I send a revert patch?  I don't think what we
> have here is acceptable going forward or being backported to stable.
> Thanks,

I didn't plan to, no. So far we *only* know of acceptable uses of RMRR
on graphics devices, and the false positives that Linda mentioned.

The only cases we ever saw of RMRR being *problematic* when we tried
to assign devices to guests were non-graphics devices, weren't they?

Although obviously I'm looking into the oops that sl4ever reported;
currently I'm wondering if that was broken even before your patch that
blacklisted all RMRR-afflicted devices. It looks like
device_to_iommu() doesn't return the correct results for devices
behind a disabled IOMMU; it incorrectly attributes them to a catch-all
IOMMU instead.

Or perhaps this is probably tied into the fact that your patch broke
iommu=pt for RMRR-afflicted devices too. They currently get full
translation. Which surely shouldn't be necessary, since passthrough
mode would obviously *also* preserve the RMRR regions of 1:1 mappings.
-- 
dwmw2

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