[Intel-gfx] [PATCH] drm/i915/guc: Document that the ads blob entries only lie within the first page

[Chris Wilson]

On Thu, Mar 16, 2017 at 10:55:06AM +0000, Chris Wilson wrote:
> guc_addon_create() makes the assumption that it need only kmap the
> initial page in order to write all of the configuration data used by the
> guc. Confusingly it also allocates many scratch pages in the same vma
> and passes that to the guc. Reassure the reader that all is well with a
> BUILD_BUG_ON() that we do not access outside of the kmapped page.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Oscar Mateo <oscar.mateo at intel.com>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_guc_submission.c | 5 +++++
>  drivers/gpu/drm/i915/i915_utils.h          | 1 +
>  2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
> index 97726fcb1230..91d7ab0df0cd 100644
> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> @@ -888,13 +888,16 @@ static void guc_addon_create(struct intel_guc *guc)
>  		guc->ads_vma = vma;
>  	}
>  
> +	/* First members are assumed to be in a single page */

s/First/Written/

>  	page = i915_vma_first_page(vma);
>  	blob = kmap(page);
>  
>  	/* GuC scheduling policies */
> +	BUILD_BUG_ON(ptr_offset_end(blob, policies) > PAGE_SIZE);
>  	guc_policies_init(&blob->policies);
>  
>  	/* MMIO reg state */
> +	BUILD_BUG_ON(ptr_offset_end(blob, reg_state) > PAGE_SIZE);
>  	for_each_engine(engine, dev_priv, id) {
>  		blob->reg_state.mmio_white_list[engine->guc_id].mmio_start =
>  			engine->mmio_base + GUC_MMIO_WHITE_LIST_START;
> @@ -903,6 +906,8 @@ static void guc_addon_create(struct intel_guc *guc)
>  		blob->reg_state.mmio_white_list[engine->guc_id].count = 0;
>  	}
>  
> +	BUILD_BUG_ON(ptr_offset_end(blob, reg_state) > PAGE_SIZE);
> +
>  	/*
>  	 * The GuC requires a "Golden Context" when it reinitialises
>  	 * engines after a reset. Here we use the Render ring default

-- 
Chris Wilson, Intel Open Source Technology Centre