[PATCH v3 2/2] drm/i915/gvt: check ggtt entry modification status for guest ctxs

[Tian, Kevin]

> From: Yan Zhao
> Sent: Friday, March 13, 2020 5:15 PM
> 
> for guest context, if its ggtt entry is modified after last context
> shadowing, it is deemed as not the same context as last shadowed one.
> 
> v3: no change
> v2: rebased to 5.6.0-rc4+
> 
> Suggested-by: Zhenyu Wang <zhenyuw at linux.intel.com>
> Signed-off-by: Yan Zhao <yan.y.zhao at intel.com>
> ---
>  drivers/gpu/drm/i915/gvt/gtt.c       | 17 +++++++++++++++++
>  drivers/gpu/drm/i915/gvt/gvt.h       |  3 ++-
>  drivers/gpu/drm/i915/gvt/scheduler.c | 14 ++++++++++++--
>  3 files changed, 31 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> index 2a4b23f8aa74..b1b6a51c006a 100644
> --- a/drivers/gpu/drm/i915/gvt/gtt.c
> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> @@ -2341,12 +2341,29 @@ int intel_vgpu_emulate_ggtt_mmio_write(struct
> intel_vgpu *vgpu,
>  {
>  	const struct intel_gvt_device_info *info = &vgpu->gvt->device_info;
>  	int ret;
> +	struct intel_vgpu_submission *s = &vgpu->submission;
> +	struct intel_engine_cs *engine;
> +	int i;
> 
>  	if (bytes != 4 && bytes != 8)
>  		return -EINVAL;
> 
>  	off -= info->gtt_start_offset;
>  	ret = emulate_ggtt_mmio_write(vgpu, off, p_data, bytes);
> +
> +	/* if ggtt of last submitted context is written,
> +	 * that context is probably got unpinned.
> +	 * Set last shadowed ctx to invalid.
> +	 */
> +	for_each_engine(engine, vgpu->gvt->gt->i915, i) {
> +		if (!s->last_ctx[i].valid)
> +			continue;
> +
> +		if (atomic_read(&s->last_ctx[i].lrca) ==
> +				off >> info->gtt_entry_size_shift) {
> +			s->last_ctx[i].valid = false;
> +		}

the context has multiple pages. Is it sufficient to compare
just the first entry?

> +	}
>  	return ret;
>  }
> 
> diff --git a/drivers/gpu/drm/i915/gvt/gvt.h b/drivers/gpu/drm/i915/gvt/gvt.h
> index e2d7ffd84457..b342d7be741f 100644
> --- a/drivers/gpu/drm/i915/gvt/gvt.h
> +++ b/drivers/gpu/drm/i915/gvt/gvt.h
> @@ -164,7 +164,8 @@ struct intel_vgpu_submission {
>  	int virtual_submission_interface;
>  	bool active;
>  	struct {
> -		u32 lrca;
> +		atomic_t lrca;
> +		bool valid;

It's not a good patch split exercise. The type should be finalized from
the start.

>  		u64 ring_context_gpa;
>  	} last_ctx[I915_NUM_ENGINES];
>  };
> diff --git a/drivers/gpu/drm/i915/gvt/scheduler.c
> b/drivers/gpu/drm/i915/gvt/scheduler.c
> index a66050a3d65a..7e0d4183b07b 100644
> --- a/drivers/gpu/drm/i915/gvt/scheduler.c
> +++ b/drivers/gpu/drm/i915/gvt/scheduler.c
> @@ -138,6 +138,7 @@ static int populate_shadow_context(struct
> intel_vgpu_workload *workload)
>  	int i;
>  	bool skip = false;
>  	int ring_id = workload->engine->id;
> +	bool valid;
> 
>  	page = i915_gem_object_get_page(ctx_obj, LRC_STATE_PN);
>  	shadow_ring_context = kmap(page);
> @@ -179,13 +180,20 @@ static int populate_shadow_context(struct
> intel_vgpu_workload *workload)
>  			workload->ctx_desc.context_id,
>  			workload->ring_context_gpa);
> 
> -	if ((s->last_ctx[ring_id].lrca ==
> +	/* only need to ensure this context is not pinned/unpinned during
> the
> +	 * period from last submission to this this submission.
> +	 * Upon reaching this function, the currently submitted context is not
> +	 * supposed to get unpinned. If a misbehaving guest driver ever does
> +	 * this, it would corrupt itself.
> +	 */
> +	valid = s->last_ctx[ring_id].valid;
> +	if (valid && (atomic_read(&s->last_ctx[ring_id].lrca) ==
>  				workload->ctx_desc.lrca) &&
>  			(s->last_ctx[ring_id].ring_context_gpa ==
>  				workload->ring_context_gpa))
>  		skip = true;
> 
> -	s->last_ctx[ring_id].lrca = workload->ctx_desc.lrca;
> +	atomic_set(&s->last_ctx[ring_id].lrca, workload->ctx_desc.lrca);
>  	s->last_ctx[ring_id].ring_context_gpa = workload->ring_context_gpa;
> 
>  	if (IS_RESTORE_INHIBIT(shadow_ring_context->ctx_ctrl.val) || skip)
> @@ -214,6 +222,8 @@ static int populate_shadow_context(struct
> intel_vgpu_workload *workload)
>  		kunmap(page);
>  		i++;
>  	}
> +	if (!valid)
> +		s->last_ctx[ring_id].valid = true;
>  	return 0;
>  }
> 
> --
> 2.17.1
> 
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