答复: 答复: [外部邮件] Re: [PATCH] iommu/dma-iommu: Fix wrong scatterlist length assignment in P2PDMA path

[Li,Rongqing]

> > Hi Li,
> >
> > On 2026-06-02 00:12, Li,Rongqing wrote:
> > >>> Fixes: a25e7962db ("PCI/P2PDMA: Refactor the p2pdma mapping
> > >>> helpers")
> > >>> Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
> > >>
> > >> Hmm, I thought I had tested this stuff pretty thoroughly so I'm
> > >> surprised I missed that. But I guess seeing the users of these
> > >> specifically don't allow mixing with anonymous memory the vast
> > >> majority of tests would only have one segment.
> > >>
> > >> Can you confirm that you've reproduced and tested this and it
> > >> actually fixes a bug? Not just seeing something that looks strange.
> > >> I have a vague feeling it was intentional but looking at the code it looks
> wrong to me too.
> > >>
> > >> Thanks,
> > >>
> > > Cc: Christoph Hellwig
> > >
> > > Thanks for your feedback!
> > >
> > > This was found via code inspection. You are right that if nents == 1, or if
> nents > 1 but all segments happen to have the exact same length, this typo
> remains benign by pure coincidence.
> > >
> > > However, for a multi-segment scatterlist with varying lengths (e.g., a short
> 2KB head segment followed by standard 4KB segments), sg_dma_len(s) will
> mistakenly assign the 2KB head length to all subsequent 4KB segments. This
> will inevitably lead to silent data truncation or IOMMU page faults.
> > >
> > > Since sg_phys(s) correctly takes the current segment's address,
> sg_dma_len(s) should definitely use s->length to match it.
> > >
> > > I don't have a specific P2PDMA test rig to force multi-segment lists on
> hand right now, but the typo and its impact on varied segment lengths seem
> deterministic.
> >
> > Ok, yeah, I think you are correct. My tests that ran multiple segments
> > happened to all have the same length. But I don't have the hardware I
> > used at the moment so I can't test it either.
> >
> > Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> 
> Rongqing can you please send a proper series with both of these fixes
> without threading so Joerg can pick them up?
> 

I think there is no need to resend.

This patch needs to be merged by Joerg

Another patch has already been merged into the DMA library.
https://git.kernel.org/pub/scm/linux/kernel/git/mszyprowski/linux.git/commit/?h=dma-mapping-fixes&id=560000d619ef162568746ce287f0c725e24ea967


[Li,Rongqing] 


> Thanks,
> Jason