Re: [Intel-gfx] [PATCH 3/7] drm/i915/uc: use different ggtt pin offsets for uc loads

[John Harrison <john.c.harrison@intel.com>]

On 9/22/2022 15:11, Daniele Ceraolo Spurio wrote:
> Our current FW loading process is the same for all FWs:
>
> - Pin FW to GGTT at the start of the ggtt->uc_fw node
> - Load the FW
> - Unpin
>
> This worked because we didn't have a case where 2 FWs would be loaded on
> the same GGTT at the same time. On MTL, however, this can happend if both
The point being that the mapping is done using a single 'dummy' vma that 
can't be mapped to two different places at the same time? But isn't 
there a separate dummy object per uc instance. So there would be one for 
the GuC on the render GT and another for the GuC on the media GT. So 
each would be mapped separately to it's own unique address and there is 
no conflict? Or what am I missing?

> GTs are reset at the same time, so we can't pin everything in the same
> spot and we need to use separate offset. For simplicity, instead of
> calculating the exact required size, we reserve a 2MB slot for each fw.
>
> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
> Cc: John Harrison <john.c.harrison@intel.com>
> Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c | 22 +++++++++++++++++++---
>   1 file changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
> index b91ad4aede1f..d6ca772e9f4b 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
> @@ -666,16 +666,33 @@ int intel_uc_fw_fetch(struct intel_uc_fw *uc_fw)
>   	return err;
>   }
>   
> +/*
> + * The reserved GGTT space is ~18 MBs. All our blobs are well below 1MB, so for
> + * safety we reserve 2MB each.
> + */
> +#define INTEL_UC_RSVD_GGTT_PER_FW SZ_2M
>   static u32 uc_fw_ggtt_offset(struct intel_uc_fw *uc_fw)
>   {
> -	struct i915_ggtt *ggtt = __uc_fw_to_gt(uc_fw)->ggtt;
> +	struct intel_gt *gt = __uc_fw_to_gt(uc_fw);
> +	struct i915_ggtt *ggtt = gt->ggtt;
>   	struct drm_mm_node *node = &ggtt->uc_fw;
> +	u32 offset = uc_fw->type * INTEL_UC_RSVD_GGTT_PER_FW;
> +
> +	/*
> +	 * To keep the math simple, we use 8MB for the root tile and 8MB for
> +	 * the media one.
> +	 */
> +	BUILD_BUG_ON(INTEL_UC_FW_NUM_TYPES * INTEL_UC_RSVD_GGTT_PER_FW > SZ_8M);
Doesn't this need to be >= ?

> +	if (gt->type == GT_MEDIA)
> +		offset += SZ_8M;
>   
>   	GEM_BUG_ON(!drm_mm_node_allocated(node));
>   	GEM_BUG_ON(upper_32_bits(node->start));
>   	GEM_BUG_ON(upper_32_bits(node->start + node->size - 1));
> +	GEM_BUG_ON(offset + uc_fw->obj->base.size > node->size);
> +	GEM_BUG_ON(uc_fw->obj->base.size > INTEL_UC_RSVD_GGTT_PER_FW);
Given that the firmware blob is loaded from the disk and therefore under 
user control, is a BUG_ON appropriate? Although there doesn't look to be 
any obvious way to abort at this point. Could the size check be moved to 
where we actually load the firmware rather than where it is being mapped?

>   
> -	return lower_32_bits(node->start);
> +	return lower_32_bits(node->start + offset);
>   }
>   
>   static void uc_fw_bind_ggtt(struct intel_uc_fw *uc_fw)
> @@ -690,7 +707,6 @@ static void uc_fw_bind_ggtt(struct intel_uc_fw *uc_fw)
>   	dummy->bi.pages = obj->mm.pages;
>   
>   	GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
> -	GEM_BUG_ON(dummy->node_size > ggtt->uc_fw.size);
Why remove this?

John.

>   
>   	/* uc_fw->obj cache domains were not controlled across suspend */
>   	if (i915_gem_object_has_struct_page(obj))