Re: [PATCH] drm/i915: Disable lazy PPGTT page table optimization for vGPU

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

Yesterday, Zhi was still looking if this could be fixed by a small
modification in the GVT-g side, which would be much preferred.

Zhi, What's the status there?

Regards, Joonas

On Thu, 2017-10-19 at 10:48 +0800, Zhenyu Wang wrote:
> On 2017.10.18 13:25:43 +0300, Joonas Lahtinen wrote:
> > When running under virtualization (vGPU active), we must disable
> > the azy PPGTT page table initialization optimization introduced by:
> > 
> > 14826673247e ("drm/i915: Only initialize partially filled pagetables")
> > 
> > We must do this because GVT-g makes unduly assumptions about guest
> > behaviour, which this optimization breaks. This results in following
> > looking errors in the host:
> > 
> > ERROR gvt: guest page write error -22, gfn 0x7ada8, pa 0x7ada89a8, var 0x6, len 1
> > 
> > The real fix is to not to depend on i915 driver behaviour, but instead
> > either rely on only the contracts that i915 has with the hardware, or
> > add some paravirtualization. While the real fix is en route, it won't
> > be finished in time for 4.15, so the best option is to disable the
> > optimization for now when vGPU is active to avoid breaking 4.15 guests
> > in existing VM environments.
> > 
> > Fixes: 14826673247e ("drm/i915: Only initialize partially filled pagetables")
> > Suggested-by: Xiaolin Zhang <xiaolin.zhang@intel.com>
> > Signed-off-by: Xiaolin Zhang <xiaolin.zhang@intel.com>
> > [Joonas: Rewrote the commit message and added tags.]
> > Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
> > Cc: Zhi Wang <zhi.a.wang@intel.com>
> > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Matthew Auld <matthew.auld@intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > Cc: Jani Nikula <jani.nikula@linux.intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>

<SNIP>
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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