linux-kernel - Re: [PATCH] iommu/amd: fix sg->dma_address for sg->offset bigger than PAGE

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Date:   Tue, 12 Mar 2019 08:08:33 +0100
From:   Stanislaw Gruszka <sgruszka@...hat.com>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Cc:     Rosen Penev <rosenp@...il.com>, Joerg Roedel <joro@...tes.org>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Samuel Sieb <samuel@...b.net>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, jan.viktorin@...il.com
Subject: Re: [PATCH] iommu/amd: fix sg->dma_address for sg->offset bigger
 than PAGE_SIZE

On Mon, Mar 11, 2019 at 08:47:44AM -0700, Alexander Duyck wrote:
> >  drivers/iommu/amd_iommu.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
> > index 6b0760dafb3e..949621f33624 100644
> > --- a/drivers/iommu/amd_iommu.c
> > +++ b/drivers/iommu/amd_iommu.c
> > @@ -2604,7 +2604,7 @@ static int map_sg(struct device *dev, struct scatterlist *sglist,
> >  
> >  	/* Everything is mapped - write the right values into s->dma_address */
> >  	for_each_sg(sglist, s, nelems, i) {
> > -		s->dma_address += address + s->offset;
> > +		s->dma_address += address + (s->offset & ~PAGE_MASK);
> >  		s->dma_length   = s->length;
> >  	}
> >  
> 
> You should add a comment calling out that this is needed because the
> sg_phys(s) call above this is masked with PAGE_MASK. Then this makes
> much more sense. Otherwise I would have assumed you needed either the
> full offset or none.

Would something like this 

/*
 * Everything is mapped - write the right values into s->dma_address. 
 * Take into account s->offset can be bigger than page size and sg_phys(s)
 * address has to be aligned to page granularity.
 */

be appropriate ?

Stanislaw