linux-kernel - Re: [PATCH v2] drm/panthor: Fix handling of partial GPU mapping of BOs

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Message-ID: <20241112100836.57fcfd5f@collabora.com>
Date: Tue, 12 Nov 2024 10:08:36 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Akash Goel <akash.goel@....com>
Cc: liviu.dudau@....com, steven.price@....com,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 mihail.atanassov@....com, ketil.johnsen@....com,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 airlied@...il.com, daniel@...ll.ch, nd@....com
Subject: Re: [PATCH v2] drm/panthor: Fix handling of partial GPU mapping of
 BOs

On Mon, 11 Nov 2024 13:47:20 +0000
Akash Goel <akash.goel@....com> wrote:

> This commit fixes the bug in the handling of partial mapping of the
> buffer objects to the GPU, which caused kernel warnings.
> 
> Panthor didn't correctly handle the case where the partial mapping
> spanned multiple scatterlists and the mapping offset didn't point
> to the 1st page of starting scatterlist. The offset variable was
> not cleared after reaching the starting scatterlist.
> 
> Following warning messages were seen.
> WARNING: CPU: 1 PID: 650 at drivers/iommu/io-pgtable-arm.c:659 __arm_lpae_unmap+0x254/0x5a0
> <snip>
> pc : __arm_lpae_unmap+0x254/0x5a0
> lr : __arm_lpae_unmap+0x2cc/0x5a0
> <snip>
> Call trace:
>  __arm_lpae_unmap+0x254/0x5a0
>  __arm_lpae_unmap+0x108/0x5a0
>  __arm_lpae_unmap+0x108/0x5a0
>  __arm_lpae_unmap+0x108/0x5a0
>  arm_lpae_unmap_pages+0x80/0xa0
>  panthor_vm_unmap_pages+0xac/0x1c8 [panthor]
>  panthor_gpuva_sm_step_unmap+0x4c/0xc8 [panthor]
>  op_unmap_cb.isra.23.constprop.30+0x54/0x80
>  __drm_gpuvm_sm_unmap+0x184/0x1c8
>  drm_gpuvm_sm_unmap+0x40/0x60
>  panthor_vm_exec_op+0xa8/0x120 [panthor]
>  panthor_vm_bind_exec_sync_op+0xc4/0xe8 [panthor]
>  panthor_ioctl_vm_bind+0x10c/0x170 [panthor]
>  drm_ioctl_kernel+0xbc/0x138
>  drm_ioctl+0x210/0x4b0
>  __arm64_sys_ioctl+0xb0/0xf8
>  invoke_syscall+0x4c/0x110
>  el0_svc_common.constprop.1+0x98/0xf8
>  do_el0_svc+0x24/0x38
>  el0_svc+0x34/0xc8
>  el0t_64_sync_handler+0xa0/0xc8
>  el0t_64_sync+0x174/0x178
> <snip>
> panthor : [drm] drm_WARN_ON(unmapped_sz != pgsize * pgcount)
> WARNING: CPU: 1 PID: 650 at drivers/gpu/drm/panthor/panthor_mmu.c:922 panthor_vm_unmap_pages+0x124/0x1c8 [panthor]
> <snip>
> pc : panthor_vm_unmap_pages+0x124/0x1c8 [panthor]
> lr : panthor_vm_unmap_pages+0x124/0x1c8 [panthor]
> <snip>
> panthor : [drm] *ERROR* failed to unmap range ffffa388f000-ffffa3890000 (requested range ffffa388c000-ffffa3890000)
> 
> Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
> Reviewed-by: Liviu Dudau <liviu.dudau@....com>
> Reviewed-by: Steven Price <steven.price@....com>
> Signed-off-by: Akash Goel <akash.goel@....com>

Oops, sorry, didn't notice the v2 before adding my R-b on v1.

Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>

> ---
>  drivers/gpu/drm/panthor/panthor_mmu.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> index d8cc9e7d064e..8d05124793f5 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -989,6 +989,8 @@ panthor_vm_map_pages(struct panthor_vm *vm, u64 iova, int prot,
>  
>  		if (!size)
>  			break;
> +
> +		offset = 0;
>  	}
>  
>  	return panthor_vm_flush_range(vm, start_iova, iova - start_iova);