RE: [PATCH v3 4/7] iommu: Switch gather->end to unsigned long long

[David Laight <David.Laight@ACULAB.COM>]

From: Yong Wu
> Sent: 16 December 2020 10:36
> 
> Currently gather->end is "unsigned long" which may be overflow in
> arch32 in the corner case: 0xfff00000 + 0x100000(iova + size).
> Although it doesn't affect the size(end - start), it affects the checking
> "gather->end < end"
> 
> Fixes: a7d20dc19d9e ("iommu: Introduce struct iommu_iotlb_gather for batching TLB flushes")
> Signed-off-by: Yong Wu <yong.wu@mediatek.com>
> ---
>  include/linux/iommu.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 794d4085edd3..6e907a95d981 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -178,7 +178,7 @@ enum iommu_dev_features {
>   */
>  struct iommu_iotlb_gather {
>  	unsigned long		start;
> -	unsigned long		end;
> +	unsigned long long	end;
>  	size_t			pgsize;
>  };

Doesn't that add two pad words on many 32bit systems?
You probably ought to re-order the structure to keep the fields
on their natural boundaries.

I'm not sure what is being mapped here, but could it make sense
to just avoid using the highest addresses?
Then you never hit the problem.

	David

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