Re: [Xen-devel] [v6][PATCH 2/2] xen:vtd: missing RMRR mapping while share EPT

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.09.14 at 02:28, <kevin.tian@xxxxxxxxx> wrote:
> I'm a bit lost what's the exact regression here. This patch definitely is 
> not aimed
> to solve all the problems, which is what Tiejun's another big series is 
> doing. it's
> a step forward to allow GPU pass-through for Windows VM, w/o regression in 
> other areas (which are mostly broken today). However, seems your regression
> is caused by patching other code:
> 
> ----
> So I gave this a try on the one box I have which exposes RMRRs
> (since those are for USB devices I also used your patch to drop
> the USB special casing as done in your later patch series, and I
> further had to fiddle with vtd_ept_page_compatible() in order to
> get page table sharing to actually work on that box [I'll send the
> resulting patch later])
> ----
> 
> If that's the case, it's not the regression typically defined.

Sure - I had to do this extra patching to have a way to simulate
the effect. I simply don't have another system where RMRRs
would be associated with other than USB devices.

The facts about the 2 patches here are:
- they don't generally help (namely not for large enough guests)
- they may yield devices unassignable that used to work fine

Jan


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