[Intel-gfx] [PATCH] drm/i915: Don't prefault the entire obj if the vma is smaller

[Chris Wilson]

On Tue, Jun 17, 2014 at 09:03:00PM +0300, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Take the minimum of the object size and the vma size and prefault
> only that much. Avoids a SIGBUS when mmapping only a portion of the
> object.
> 
> Prefaulting was introduced here:
>  commit b90b91d87038f6b257b40a02b42ed4f9705e06f0
>  Author: Chris Wilson <chris at chris-wilson.co.uk>
>  Date:   Tue Jun 10 12:14:40 2014 +0100
> 
>     drm/i915: Prefault the entire object on first page fault
> 
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 6f8c206..4ef80d1 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1578,9 +1578,12 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>  	pfn >>= PAGE_SHIFT;
>  
>  	if (!obj->fault_mappable) {
> +		unsigned long size = min_t(unsigned long,
> +					   vma->vm_end - vma->vm_start,
> +					   obj->base.size);

The vma should be the same size as the obj... Unless it gets
coalesced... I wonder if that is even legal for our objects because I
was under the impression that we depended upon it in other places.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre