Re: [PATCH v1] drm/i915/guc: Fix a fw content lost issue after it is evicted

[Chris Wilson <chris@chris-wilson.co.uk>]

On Tue, Nov 10, 2015 at 03:27:36PM -0800, yu.dai@intel.com wrote:
> From: Alex Dai <yu.dai@intel.com>
> 
> We keep a copy of GuC fw in a GEM obj. However its content is lost
> if the GEM obj is swapped (igt/gem_evict_*). Therefore, the later
> fw loading during GPU reset will fail. Mark the obj dirty after
> copying data into the pages. So its content will be kept during
> swapped out.
> 
> Signed-off-by: Alex Dai <yu.dai@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index f1e3fde..3b15167 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -5199,6 +5199,7 @@ i915_gem_object_create_from_data(struct drm_device *dev,
>  	i915_gem_object_pin_pages(obj);
>  	sg = obj->pages;
>  	bytes = sg_copy_from_buffer(sg->sgl, sg->nents, (void *)data, size);
> +	obj->dirty = 1;

That's one way of doing it, but atypical for our CPU access to the pages.
The root cause is still that sg_copy_from_buffer() isn't calling
set_page_dirty() and so there will be other places in the kernel that
fall foul of it. Also, not that we could have written this to not require
the whole object to be pinned at once as well.

I would prefer this to be fixed in sg_copy_from_buffer() for the reason
that all callers are susceptible to this bug.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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