[PATCH] drm/xe/bmg: fix compressed VRAM handling

[Cavitt, Jonathan]

-----Original Message-----
From: Intel-xe <intel-xe-bounces at lists.freedesktop.org> On Behalf Of Matthew Auld
Sent: Wednesday, June 4, 2025 11:15 AM
To: intel-xe at lists.freedesktop.org
Cc: Ghimiray, Himal Prasad <himal.prasad.ghimiray at intel.com>; Thomas Hellström <thomas.hellstrom at linux.intel.com>; Jahagirdar, Akshata <akshata.jahagirdar at intel.com>; stable at vger.kernel.org
Subject: [PATCH] drm/xe/bmg: fix compressed VRAM handling
> 
> There looks to be an issue in our compression handling when the BO pages
> are very fragmented, where we choose to skip the identity map and
> instead fall back to emitting the PTEs by hand when migrating memory,
> such that we can hopefully do more work per blit operation. However in
> such a case we need to ensure the src PTEs are correctly tagged with a
> compression enabled PAT index on dgpu xe2+, otherwise the copy will
> simply treat the src memory as uncompressed, leading to corruption if
> the memory was compressed by the user.
> 
> To fix this it looks like we can pass use_comp_pat into emit_pte() on
> the src side.

It would be better if we had more confidence here beyond "it looks like"
(maybe just drop that part) and "There looks to be" (maybe "There is" instead),
but if we're not comfortable making definitive statements about our compression
handling, then I won't block this on some minor passive voice issues.
Reviewed-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
-Jonathan Cavitt

> 
> There are reports of VRAM corruption in some heavy user workloads, which
> might be related: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/4495
> 
> Fixes: 523f191cc0c7 ("drm/xe/xe_migrate: Handle migration logic for xe2+ dgfx")
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray at intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Akshata Jahagirdar <akshata.jahagirdar at intel.com>
> Cc: <stable at vger.kernel.org> # v6.12+
> ---
>  drivers/gpu/drm/xe/xe_migrate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_migrate.c b/drivers/gpu/drm/xe/xe_migrate.c
> index 8f8e9fdfb2a8..16788ecf924a 100644
> --- a/drivers/gpu/drm/xe/xe_migrate.c
> +++ b/drivers/gpu/drm/xe/xe_migrate.c
> @@ -863,7 +863,7 @@ struct dma_fence *xe_migrate_copy(struct xe_migrate *m,
>  		if (src_is_vram && xe_migrate_allow_identity(src_L0, &src_it))
>  			xe_res_next(&src_it, src_L0);
>  		else
> -			emit_pte(m, bb, src_L0_pt, src_is_vram, copy_system_ccs,
> +			emit_pte(m, bb, src_L0_pt, src_is_vram, copy_system_ccs || use_comp_pat,
>  				 &src_it, src_L0, src);
>  
>  		if (dst_is_vram && xe_migrate_allow_identity(src_L0, &dst_it))
> -- 
> 2.49.0
> 
>