[Intel-gfx] [PATCH] drm/i915: Fix mismatch between misplaced vma check and vma insert

[Tang, CQ]

> -----Original Message-----
> From: Chris Wilson <chris at chris-wilson.co.uk>
> Sent: Tuesday, December 15, 2020 12:31 PM
> To: intel-gfx at lists.freedesktop.org
> Cc: Chris Wilson <chris at chris-wilson.co.uk>; Tang, CQ <cq.tang at intel.com>;
> stable at vger.kernel.org
> Subject: [PATCH] drm/i915: Fix mismatch between misplaced vma check and
> vma insert
> 
> When inserting a VMA, we restrict the placement to the low 4G unless the
> caller opts into using the full range. This was done to allow usersapce the
> opportunity to transition slowly from a 32b address space, and to avoid
> breaking inherent 32b assumptions of some commands.
> 
> However, for insert we limited ourselves to 4G-4K, but on verification we
> allowed the full 4G. This causes some attempts to bind a new buffer to
> sporadically fail with -ENOSPC, but at other times be bound successfully.
> 
> commit 48ea1e32c39d ("drm/i915/gen9: Set PIN_ZONE_4G end to 4GB - 1
> page") suggests that there is a genuine problem with stateless addressing
> that cannot utilize the last page in 4G and so we purposefully excluded it.
> 
> Reported-by: CQ Tang <cq.tang at intel.com>
> Fixes: 48ea1e32c39d ("drm/i915/gen9: Set PIN_ZONE_4G end to 4GB - 1
> page")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: CQ Tang <cq.tang at intel.com>
> Cc: stable at vger.kernel.org
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 193996144c84..2ff32daa50bd 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -382,7 +382,7 @@ eb_vma_misplaced(const struct
> drm_i915_gem_exec_object2 *entry,
>  		return true;
> 
>  	if (!(flags & EXEC_OBJECT_SUPPORTS_48B_ADDRESS) &&
> -	    (vma->node.start + vma->node.size - 1) >> 32)
> +	    (vma->node.start + vma->node.size + 4095) >> 32)

Why 4095 not 4096?

--CQ

>  		return true;
> 
>  	if (flags & __EXEC_OBJECT_NEEDS_MAP &&
> --
> 2.20.1