[Intel-gfx] [PATCH] drm/i915: Disable lazy PPGTT page table optimization for vGPU

[Wang, Zhi A]

Hi Joonas
    Better you can take this patch first, since I was still stuck in floods of creating invalid entries in page table.

Thanks,
Zhi.

-----Original Message-----
From: Joonas Lahtinen [mailto:joonas.lahtinen at linux.intel.com] 
Sent: Friday, October 20, 2017 12:04 PM
To: Zhenyu Wang <zhenyuw at linux.intel.com>; Wang, Zhi A <zhi.a.wang at intel.com>
Cc: Intel graphics driver community testing & development <intel-gfx at lists.freedesktop.org>; Zhang, Xiaolin <xiaolin.zhang at intel.com>; Chris Wilson <chris at chris-wilson.co.uk>; Auld, Matthew <matthew.auld at intel.com>; Jani Nikula <jani.nikula at linux.intel.com>; Vivi, Rodrigo <rodrigo.vivi at intel.com>
Subject: Re: [PATCH] drm/i915: Disable lazy PPGTT page table optimization for vGPU

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 at intel.com>
> > Signed-off-by: Xiaolin Zhang <xiaolin.zhang at intel.com>
> > [Joonas: Rewrote the commit message and added tags.]
> > Signed-off-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > Cc: Zhenyu Wang <zhenyuw at linux.intel.com>
> > Cc: Zhi Wang <zhi.a.wang at intel.com>
> > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Matthew Auld <matthew.auld at intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > Cc: Jani Nikula <jani.nikula at linux.intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>

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