Re: [PATCH RFC] iommu/mediatek: Flush IOTLB completely only if domain has been attached

["Yong Wu (吴勇)" <Yong.Wu@mediatek.com>]

On Fri, 2023-05-26 at 16:53 +0800, Chen-Yu Tsai wrote:
>  	 
>  If an IOMMU domain was never attached, it lacks any linkage to the
> actual IOMMU hardware. Attempting to do flush_iotlb_all() on it will
> result in a NULL pointer dereference. This seems to happen after the
> recent IOMMU core rework in v6.4-rc1.
> 
>     Unable to handle kernel read from unreadable memory at virtual
> address 0000000000000018
>     Call trace:
>      mtk_iommu_flush_iotlb_all+0x20/0x80
>      iommu_create_device_direct_mappings.part.0+0x13c/0x230
>      iommu_setup_default_domain+0x29c/0x4d0
>      iommu_probe_device+0x12c/0x190
>      of_iommu_configure+0x140/0x208
>      of_dma_configure_id+0x19c/0x3c0
>      platform_dma_configure+0x38/0x88
>      really_probe+0x78/0x2c0
> 
> Check if the "bank" field has been filled in before actually
> attempting
> the IOTLB flush to avoid it. The IOTLB is also flushed when the
> device
> comes out of runtime suspend, so it should have a clean initial
> state.
> 
> Fixes: 08500c43d4f7 ("iommu/mediatek: Adjust the structure")

The interface "iommu_setup_default_domain" doesn't exist in v6.4-rc1.

This is a fixes for linux-next. And the Fixes tag should be:

152431e4fe7f ("iommu: Do iommu_group_create_direct_mappings() before
attach")

then: 
Reviewed-by: Yong Wu <yong.wu@mediatek.com>

Thanks very much.

> Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
> ---
> 
> I think this is a valid fix, but I'm not very familiar with the
> hardware
> or the design of the driver. The ARM SMMU drivers seem to do this as
> well.
> 
>  drivers/iommu/mtk_iommu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index aecc7d154f28..e93906d6e112 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -781,7 +781,8 @@ static void mtk_iommu_flush_iotlb_all(struct
> iommu_domain *domain)
>  {
>  	struct mtk_iommu_domain *dom = to_mtk_domain(domain);
>  
> -	mtk_iommu_tlb_flush_all(dom->bank->parent_data);
> +	if (dom->bank)
> +		mtk_iommu_tlb_flush_all(dom->bank->parent_data);
>  }
>  
>  static void mtk_iommu_iotlb_sync(struct iommu_domain *domain,
> -- 
> 2.41.0.rc0.172.g3f132b7071-goog