Re: [PATCH 4/4] drm/xe: Keep VRAM fault injection within the usable range

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] xe: unaligned VRAM fault injection address on PAGE_SIZE > 4K
--

commit ec0c39c567f41b1c9847a4f7270a2e926f7a5f9b
Author: Tejas Upadhyay <tejas.upadhyay@intel.com>
Subject: drm/xe: Keep VRAM fault injection within the usable range

This commit changes the fault injection probe in xe_ttm_vram_inject_fault()
to start at vr->usable_size rather than vr->actual_physical_size. This keeps
the injected faults within the buddy-managed VRAM range instead of hitting
the CCS/GSM/DSM infrastructure zone.

> diff --git a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> index 7211ab5f66e9b..ec15eab1a2edb 100644
> --- a/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> +++ b/drivers/gpu/drm/xe/xe_ttm_vram_mgr.c
> @@ -988,11 +988,12 @@ int xe_ttm_vram_inject_fault(struct xe_device *xe)
>  	struct gpu_buddy *mm = &vram_mgr->mm;
>  	u64 addr;
>  
> -	if (vr->actual_physical_size < PAGE_SIZE)
> +	/* Stay within the buddy-managed range; CCS/GSM/DSM sit beyond usable_size */
> +	if (vr->usable_size < PAGE_SIZE)
>  		return -ENOSPC;
>  
> -	addr = vr->actual_physical_size - PAGE_SIZE;
> -	while (addr < vr->actual_physical_size) {
> +	addr = vr->usable_size - PAGE_SIZE;

[Severity: Medium]
Will this result in an unaligned VRAM fault injection address on systems where
PAGE_SIZE > 4K (e.g., ARM64)?

Since vr->usable_size is only guaranteed to be 4K aligned (via 
round_down(offset, SZ_4K) in get_flat_ccs_offset()), subtracting a larger 
PAGE_SIZE here would produce an address that is not PAGE_SIZE aligned.

If this unaligned address is subsequently passed to 
xe_ttm_vram_handle_addr_fault(), will it trigger a WARN_ON_ONCE and fail 
the fault injection test with -EINVAL, effectively breaking the debugfs 
interface on these architectures?

> +	while (addr < vr->usable_size) {
>  		struct gpu_buddy_block *block;
>  		bool found = false;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261001094518.1493651-6-tejas.upadhyay@intel.com?part=4