[PATCH 1/2] drm/i915/gvt: reorder the shadow ppgtt update process by adding entry first

[Zhi Wang]

于 05/09/17 10:22, Tina Zhang 写道:
> Guest i915 driver may update the ppgtt table just before this workload
> is going to be submitted to the hardware by device model. This case
> wasn't handled well by device model before, due to the small time
> window between removing old ppgtt entry and adding the new one. Errors
> occur when the workload is executed by hardware during that small time
> window. This patch is to remove this time window by adding the new ppgtt
> entry first and then remove the old one.
>
> v2. add some comments. (Zhi) (Zhenyu)
>
> Signed-off-by: Tina Zhang <tina.zhang at intel.com>
>
> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> index c6f0077..1b91e69 100644
> --- a/drivers/gpu/drm/i915/gvt/gtt.c
> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> @@ -975,29 +975,26 @@ static int ppgtt_populate_shadow_page(struct intel_vgpu_ppgtt_spt *spt)
>   }
>   
>   static int ppgtt_handle_guest_entry_removal(struct intel_vgpu_guest_page *gpt,
> -		unsigned long index)
> +		struct intel_gvt_gtt_entry *se, unsigned long index)
>   {
>   	struct intel_vgpu_ppgtt_spt *spt = guest_page_to_ppgtt_spt(gpt);
>   	struct intel_vgpu_shadow_page *sp = &spt->shadow_page;
>   	struct intel_vgpu *vgpu = spt->vgpu;
>   	struct intel_gvt_gtt_pte_ops *ops = vgpu->gvt->gtt.pte_ops;
> -	struct intel_gvt_gtt_entry e;
>   	int ret;
>   
> -	ppgtt_get_shadow_entry(spt, &e, index);
> -
> -	trace_gpt_change(spt->vgpu->id, "remove", spt, sp->type, e.val64,
> +	trace_gpt_change(spt->vgpu->id, "remove", spt, sp->type, se->val64,
>   			 index);
>   
> -	if (!ops->test_present(&e))
> +	if (!ops->test_present(se))
>   		return 0;
>   
> -	if (ops->get_pfn(&e) == vgpu->gtt.scratch_pt[sp->type].page_mfn)
> +	if (ops->get_pfn(se) == vgpu->gtt.scratch_pt[sp->type].page_mfn)
>   		return 0;
>   
> -	if (gtt_type_is_pt(get_next_pt_type(e.type))) {
> +	if (gtt_type_is_pt(get_next_pt_type(se->type))) {
>   		struct intel_vgpu_ppgtt_spt *s =
> -			ppgtt_find_shadow_page(vgpu, ops->get_pfn(&e));
> +			ppgtt_find_shadow_page(vgpu, ops->get_pfn(se));
>   		if (!s) {
>   			gvt_vgpu_err("fail to find guest page\n");
>   			ret = -ENXIO;
> @@ -1007,12 +1004,10 @@ static int ppgtt_handle_guest_entry_removal(struct intel_vgpu_guest_page *gpt,
>   		if (ret)
>   			goto fail;
>   	}
> -	ops->set_pfn(&e, vgpu->gtt.scratch_pt[sp->type].page_mfn);
> -	ppgtt_set_shadow_entry(spt, &e, index);
>   	return 0;
>   fail:
>   	gvt_vgpu_err("fail: shadow page %p guest entry 0x%llx type %d\n",
> -			spt, e.val64, e.type);
> +			spt, se->val64, se->type);
>   	return ret;
>   }
>   
> @@ -1232,22 +1227,39 @@ static int ppgtt_handle_guest_write_page_table(
>   {
>   	struct intel_vgpu_ppgtt_spt *spt = guest_page_to_ppgtt_spt(gpt);
>   	struct intel_vgpu *vgpu = spt->vgpu;
> +	int type = spt->shadow_page.type;
>   	struct intel_gvt_gtt_pte_ops *ops = vgpu->gvt->gtt.pte_ops;
> +	struct intel_gvt_gtt_entry se;
>   
>   	int ret;
>   	int new_present;
>   
>   	new_present = ops->test_present(we);
>   
> -	ret = ppgtt_handle_guest_entry_removal(gpt, index);
> -	if (ret)
> -		goto fail;
> +	/*
> +	 * Guest i915 driver may update the ppgtt table just before the related
> +	 * workload going to be submitted to the hardware by device model. If
> +	 * the submisson is happened during the process of updating ppgtt table,
> +	 * a provision must be made for guaranteeing the validation of ppgttt,
> +	 * by adding new ppgtt entry first and then removing the old one.
> +	 */
> +	ppgtt_get_shadow_entry(spt, &se, index);
>   
As we have improved the process of shadow updating, the developer who 
might read this code will be confused. Better just introduce the process 
of building new shadow. For the background, he can find it from the 
commit message.
>   	if (new_present) {
>   		ret = ppgtt_handle_guest_entry_add(gpt, we, index);
>   		if (ret)
>   			goto fail;
>   	}
> +
> +	ret = ppgtt_handle_guest_entry_removal(gpt, &se, index);
> +	if (ret)
> +		goto fail;
> +
> +	if (!new_present) {
> +		ops->set_pfn(&se, vgpu->gtt.scratch_pt[type].page_mfn);
> +		ppgtt_set_shadow_entry(spt, &se, index);
> +	}
> +
>   	return 0;
>   fail:
>   	gvt_vgpu_err("fail: shadow page %p guest entry 0x%llx type %d.\n",
> @@ -1319,7 +1331,7 @@ static int ppgtt_handle_guest_write_page_table_bytes(void *gp,
>   	struct intel_vgpu *vgpu = spt->vgpu;
>   	struct intel_gvt_gtt_pte_ops *ops = vgpu->gvt->gtt.pte_ops;
>   	const struct intel_gvt_device_info *info = &vgpu->gvt->device_info;
> -	struct intel_gvt_gtt_entry we;
> +	struct intel_gvt_gtt_entry we, se;
>   	unsigned long index;
>   	int ret;
>   
> @@ -1335,7 +1347,8 @@ static int ppgtt_handle_guest_write_page_table_bytes(void *gp,
>   			return ret;
>   	} else {
>   		if (!test_bit(index, spt->post_shadow_bitmap)) {
> -			ret = ppgtt_handle_guest_entry_removal(gpt, index);
> +			ppgtt_get_shadow_entry(spt, &se, index);
> +			ret = ppgtt_handle_guest_entry_removal(gpt, &se, index);
>   			if (ret)
>   				return ret;
>   		}