drm/i915: Disable lazy PPGTT page table optimization for vGPU
authorJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Mon, 23 Oct 2017 15:32:09 +0000 (18:32 +0300)
committerJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Wed, 25 Oct 2017 14:24:59 +0000 (17:24 +0300)
commit22a8a4fc93b14b5a8cfc785edbdc6f7bd98bffb6
tree3174ddf38a0a8c19c9ecffae9451463f9512f2e2
parent02a1ca45cf33d23c7540b572aed5bf624ba968fe
drm/i915: Disable lazy PPGTT page table optimization for vGPU

When running under virtualization (vGPU active), we must disable
the lazy PPGTT page table initialization optimization introduced by
commit 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>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171023153209.10527-1-joonas.lahtinen@linux.intel.com
drivers/gpu/drm/i915/i915_gem_gtt.c