[Intel-gfx] [PATCH] drm/i915/gt: Fill all the unused space in the GGTT

[Imre Deak]

On Tue, Mar 31, 2020 at 01:42:02PM +0100, Chris Wilson wrote:
> When we allocate space in the GGTT we may have to allocate a larger
> region than will be populated by the object to accommodate fencing. Make
> sure that this space beyond the end of the buffer points safely into
> scratch space, in case the HW tries to access it anyway (e.g. fenced
> access to the last tile row).
> 
> Reported-by: Imre Deak <imre.deak at intel.com>
> References: https://gitlab.freedesktop.org/drm/intel/-/issues/1554
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Matthew Auld <matthew.auld at intel.com>
> Cc: Imre Deak <imre.deak at intel.com>
> Cc: stable at vger.kernel.org

Thanks,
Reviewed-by: Imre Deak <imre.deak at intel.com>

> ---
>  drivers/gpu/drm/i915/gt/intel_ggtt.c | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> index d8944dabed55..ad56059651b8 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> @@ -191,10 +191,11 @@ static void gen8_ggtt_insert_entries(struct i915_address_space *vm,
>  				     enum i915_cache_level level,
>  				     u32 flags)
>  {
> +	const gen8_pte_t pte_encode = gen8_ggtt_pte_encode(0, level, 0);
>  	struct i915_ggtt *ggtt = i915_vm_to_ggtt(vm);
>  	struct sgt_iter sgt_iter;
> -	gen8_pte_t __iomem *gtt_entries;
> -	const gen8_pte_t pte_encode = gen8_ggtt_pte_encode(0, level, 0);
> +	gen8_pte_t __iomem *gte;
> +	gen8_pte_t __iomem *end;
>  	dma_addr_t addr;
>  
>  	/*
> @@ -202,10 +203,16 @@ static void gen8_ggtt_insert_entries(struct i915_address_space *vm,
>  	 * not to allow the user to override access to a read only page.
>  	 */
>  
> -	gtt_entries = (gen8_pte_t __iomem *)ggtt->gsm;
> -	gtt_entries += vma->node.start / I915_GTT_PAGE_SIZE;
> +	gte = (gen8_pte_t __iomem *)ggtt->gsm;
> +	gte += vma->node.start / I915_GTT_PAGE_SIZE;
> +	end = gte + vma->node.size / I915_GTT_PAGE_SIZE;
>  	for_each_sgt_daddr(addr, sgt_iter, vma->pages)
> -		gen8_set_pte(gtt_entries++, pte_encode | addr);
> +		gen8_set_pte(gte++, pte_encode | addr);
> +	GEM_BUG_ON(gte > end);
> +
> +	/* Fill the allocated but "unused" space beyond the end of the buffer */
> +	while (gte < end)
> +		gen8_set_pte(gte++, vm->scratch[0].encode);
>  
>  	/*
>  	 * We want to flush the TLBs only after we're certain all the PTE
> -- 
> 2.20.1
>