[PATCH] drm/i915/gvt: Fix kernel oops for 3-level ppgtt guest

[Zhenyu Wang]

On 2020.05.08 11:13:38 +0000, Zhang, Xiong Y wrote:
> > -----Original Message-----
> > From: intel-gvt-dev <intel-gvt-dev-bounces at lists.freedesktop.org> On Behalf
> > Of Zhenyu Wang
> > Sent: Wednesday, May 6, 2020 5:59 PM
> > To: intel-gvt-dev at lists.freedesktop.org
> > Subject: [PATCH] drm/i915/gvt: Fix kernel oops for 3-level ppgtt guest
> > 
> > As i915 won't allocate extra PDP for current default PML4 table, so for 3-level
> > ppgtt guest, we would hit kernel pointer access failure on extra PDP pointers.
> > So this trys to bypass that now.
> > It won't impact real shadow PPGTT setup, so guest context still works.
> > 
> > This is verified on 4.15 guest kernel with i915.enable_ppgtt=1 to force on old
> > aliasing ppgtt behavior.
> > 
> > Fixes: 4f15665ccbba ("drm/i915: Add ppgtt to GVT GEM context")
> > Signed-off-by: Zhenyu Wang <zhenyuw at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/gvt/scheduler.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c
> > b/drivers/gpu/drm/i915/gvt/scheduler.c
> > index 9c3558489d17..6ab1d95c1fae 100644
> > --- a/drivers/gpu/drm/i915/gvt/scheduler.c
> > +++ b/drivers/gpu/drm/i915/gvt/scheduler.c
> > @@ -420,7 +420,11 @@ static void set_context_ppgtt_from_shadow(struct
> > intel_vgpu_workload *workload,
> >  		for (i = 0; i < GVT_RING_CTX_NR_PDPS; i++) {
> >  			struct i915_page_directory * const pd =
> >  				i915_pd_entry(ppgtt->pd, i);
> > -
> > +			/* skip now as current i915 ppgtt alloc won't allocate
> > +			   top level pdp for non 4-level table, won't impact
> > +			   shadow ppgtt. */
> > +			if (!pd)
> > +				break;
> [Zhang, Xiong Y]  does it  exist in older kernel only ?  current staging code allocate 4 pdp for non 4-level table.

But in all current case we'll only allocate for pml4 as it checks hw info.

> I915_context_ppgtt_root_restore()  have the same issue, it should be modified also.

yeah, missed that although not shown in my test..

> >  			px_dma(pd) = mm->ppgtt_mm.shadow_pdps[i];
> >  		}
> >  	}
> > --
> > 2.26.2
> > 
> > _______________________________________________
> > intel-gvt-dev mailing list
> > intel-gvt-dev at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev

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