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 <[email protected]>
Signed-off-by: Xiaolin Zhang <[email protected]>
[Joonas: Rewrote the commit message and added tags.]
Signed-off-by: Joonas Lahtinen <[email protected]>
Cc: Zhenyu Wang <[email protected]>
Cc: Zhi Wang <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Matthew Auld <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Rodrigo Vivi <[email protected]>
Acked-by: Chris Wilson <[email protected]>
Acked-by: Zhenyu Wang <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit 22a8a4fc93b14b5a8cfc785edbdc6f7bd98bffb6)
Signed-off-by: Jani Nikula <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 527a2d2d6281..5eaa6893daaa 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -1341,7 +1341,7 @@ static int gen8_ppgtt_alloc_pd(struct i915_address_space *vm,
 			if (IS_ERR(pt))
 				goto unwind;
 
-			if (count < GEN8_PTES)
+			if (count < GEN8_PTES || intel_vgpu_active(vm->i915))
 				gen8_initialize_pt(vm, pt);
 
 			gen8_ppgtt_set_pde(vm, pd, pt, pde);