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

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Date:   Thu, 17 Dec 2020 10:26:01 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     Robin Murphy <robin.murphy@....com>
CC:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        <youlin.pei@...iatek.com>, <anan.sun@...iatek.com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        <srv_heupstream@...iatek.com>, <chao.hao@...iatek.com>,
        <linux-kernel@...r.kernel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Tomasz Figa <tfiga@...gle.com>,
        <iommu@...ts.linux-foundation.org>,
        <linux-mediatek@...ts.infradead.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Greg Kroah-Hartman <gregkh@...gle.com>,
        <kernel-team@...roid.com>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 4/7] iommu: Switch gather->end to unsigned long long

On Wed, 2020-12-16 at 12:10 +0000, Robin Murphy wrote:
> On 2020-12-16 10:36, Yong Wu wrote:
> > 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"
> 
> This won't help the same situation at the top of a 64-bit address space, 
> though, and now that we have TTBR1 support for AArch64 format that is 
> definitely a thing. Better to just encode the end address as the actual 
> end address, i.e. iova + size - 1. We don't lose anything other than the 
> ability to encode zero-sized invalidations that don't make sense anyway.

Thanks for the suggestion. "iova + size - 1" is better. Also I will
change the "size" to "gather->end - gather->start + 1" in the iotlb_sync
of arm-smmu-v3.c and mtk_iommu.c.

> 
> Robin.
> 
> > Fixes: a7d20dc19d9e ("iommu: Introduce struct iommu_iotlb_gather for batching TLB flushes")
> > Signed-off-by: Yong Wu <yong.wu@...iatek.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;
> >   };
> >   
> > @@ -537,7 +537,8 @@ static inline void iommu_iotlb_gather_add_page(struct iommu_domain *domain,
> >   					       struct iommu_iotlb_gather *gather,
> >   					       unsigned long iova, size_t size)
> >   {
> > -	unsigned long start = iova, end = start + size;
> > +	unsigned long start = iova;
> > +	unsigned long long end = start + size;
> >   
> >   	/*
> >   	 * If the new page is disjoint from the current range or is mapped at
> >