[Intel-gfx] [PATCH] drm/i915: Add ppgtt to GVT GEM context

[Chris Wilson]

Quoting Zhenyu Wang (2018-10-19 04:05:20)
> On 2018.10.18 13:40:31 +0800, Xiong Zhang wrote:
> > Currently the guest couldn't boot up under GVT-g environment as the
> > following call trace exists:
> > [  272.504762] BUG: unable to handle kernel NULL pointer dereference at 0000000000000100
> > [  272.504834] Call Trace:
> > [  272.504852]  execlists_context_pin+0x2b2/0x520 [i915]
> > [  272.504869]  intel_gvt_scan_and_shadow_workload+0x50/0x4d0 [i915]
> > [  272.504887]  intel_vgpu_create_workload+0x3e2/0x570 [i915]
> > [  272.504901]  intel_vgpu_submit_execlist+0xc0/0x2a0 [i915]
> > [  272.504916]  elsp_mmio_write+0xc7/0x130 [i915]
> > [  272.504930]  intel_vgpu_mmio_reg_rw+0x24a/0x4c0 [i915]
> > [  272.504944]  intel_vgpu_emulate_mmio_write+0xac/0x240 [i915]
> > [  272.504947]  intel_vgpu_rw+0x22d/0x270 [kvmgt]
> > [  272.504949]  intel_vgpu_write+0x164/0x1f0 [kvmgt]
> > 
> > GVT GEM context is created by i915_gem_context_create_gvt() which
> > doesn't allocate ppgtt. So GVT GEM context structure doesn't have
> > a valid i915_hw_ppgtt.
> > 
> > This patch create ppgtt table at GVT GEM context creation, then assign
> > shadow ppgtt's root table address to this ppgtt when shadow ppgtt will
> > be used on GPU. So GVT GEM context has valid ppgtt address. But note
> > that this ppgtt only contain valid ppgtt root table address, the table
> > entry in this ppgtt structure are invalid.
> > 
> > Fixes:4a3d3f6785be("drm/i915: Match code to comment and enforce ppgtt for execlists")
> > 
> > Signed-off-by: Xiong Zhang <xiong.y.zhang at intel.com>
> > Reviewed-by: Zhenyu Wang <zhenyuw at linux.intel.com>
> 
> Any more comment for this? We need it for current gvt broken on drm-tip,
> and it requires to change i915 for gvt ppgtt allocation, so I assume it's
> better to be merged by i915 directly, or do you like a gvt pull instead?

You only needed ctx->ppgtt being set I thought, as you previously
ignored the initial PD bits in the context image and overwrote the
registers anyway.

Do you want what appears to be a significant change to gvt itself to
enter from i915?
-Chris