[Intel-gfx] [PATCH] drm/i915/mtl: Disable stolen memory backed FB for A0

[Intel-gfx] [PATCH] drm/i915/mtl: Disable stolen memory backed FB for A0

[Nirmoy Das]

Stolen memory is not usable for MTL A0 stepping beyond
certain access size and we have no control over userspace
access size of /dev/fb which can be backed by stolen memory.
So disable stolen memory backed fb by setting i915->dsm.usable_size
to zero.

Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>

Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_stolen.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
index d8e06e783e30..56ccfcbdbce1 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
@@ -535,6 +535,16 @@ static int i915_gem_init_stolen(struct intel_memory_region *mem)
 	/* Basic memrange allocator for stolen space. */
 	drm_mm_init(&i915->mm.stolen, 0, i915->dsm.usable_size);
 
+	/*
+	 * Access to stolen lmem beyond certain size for MTL A0 stepping
+	 * would crash the machine. Disable stolen lmem for userspace access
+	 * by setting usable_size to zero.
+	 * hsdes: 22016134735
+	 */
+	if (IS_MTL_GRAPHICS_STEP(i915, M, STEP_A0, STEP_B0) ||
+	    IS_MTL_GRAPHICS_STEP(i915, P, STEP_A0, STEP_B0))
+		i915->dsm.usable_size = 0;
+
 	return 0;
 }
 
-- 
2.39.0

Re: [Intel-gfx] [PATCH] drm/i915/mtl: Disable stolen memory backed FB for A0

[Andi Shyti]

Hi Nirmoy,

On Thu, Mar 09, 2023 at 05:49:05PM +0100, Nirmoy Das wrote:
> Stolen memory is not usable for MTL A0 stepping beyond
> certain access size and we have no control over userspace
> access size of /dev/fb which can be backed by stolen memory.
> So disable stolen memory backed fb by setting i915->dsm.usable_size
> to zero.
> 
> Cc: Matthew Auld <matthew.auld@intel.com>
> Cc: Andi Shyti <andi.shyti@linux.intel.com>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> 

Can you please remove this blank line from the tag space?

> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_stolen.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> index d8e06e783e30..56ccfcbdbce1 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> @@ -535,6 +535,16 @@ static int i915_gem_init_stolen(struct intel_memory_region *mem)
>  	/* Basic memrange allocator for stolen space. */
>  	drm_mm_init(&i915->mm.stolen, 0, i915->dsm.usable_size);
>  
> +	/*
> +	 * Access to stolen lmem beyond certain size for MTL A0 stepping
> +	 * would crash the machine. Disable stolen lmem for userspace access
> +	 * by setting usable_size to zero.
> +	 * hsdes: 22016134735

Please, remove this reference, as well.

With the above:

Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>

Thanks,
Andi

> +	 */
> +	if (IS_MTL_GRAPHICS_STEP(i915, M, STEP_A0, STEP_B0) ||
> +	    IS_MTL_GRAPHICS_STEP(i915, P, STEP_A0, STEP_B0))
> +		i915->dsm.usable_size = 0;
> +
>  	return 0;
>  }
>  
> -- 
> 2.39.0