linux-kernel - Re: [PATCH] iommu/dma: add missing support for DMA_ATTR_MMIO for dma_iova

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251124172038.GD12483@unreal>
Date: Mon, 24 Nov 2025 19:20:38 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Robin Murphy <robin.murphy@....com>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH] iommu/dma: add missing support for DMA_ATTR_MMIO for
 dma_iova_unlink()

On Mon, Nov 24, 2025 at 05:15:48PM +0000, Robin Murphy wrote:
> On 2025-11-24 5:09 pm, Marek Szyprowski wrote:
> > Commit c288d657dd51 added support for DMA_ATTR_MMIO attribute in the
> > dma_iova_link() code path, but missed that the CPU cache is being also
> > touched in the dma_iova_unlink() path. Fix this.
> > 
> > Fixes: c288d657dd51 ("iommu/dma: implement DMA_ATTR_MMIO for dma_iova_link().")
> > Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> > ---
> >   drivers/iommu/dma-iommu.c | 5 +++--
> >   1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index e52d19d2e833..c92088855450 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -2008,7 +2008,7 @@ static void iommu_dma_iova_unlink_range_slow(struct device *dev,
> >   			end - addr, iovad->granule - iova_start_pad);
> >   		if (!dev_is_dma_coherent(dev) &&
> > -		    !(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> > +		    !(attrs & (DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_MMIO)))
> >   			arch_sync_dma_for_cpu(phys, len, dir);
> >   		swiotlb_tbl_unmap_single(dev, phys, len, dir, attrs);
> > @@ -2032,7 +2032,8 @@ static void __iommu_dma_iova_unlink(struct device *dev,
> >   	size_t unmapped;
> >   	if ((state->__size & DMA_IOVA_USE_SWIOTLB) ||
> > -	    (!dev_is_dma_coherent(dev) && !(attrs & DMA_ATTR_SKIP_CPU_SYNC)))
> > +	    (!dev_is_dma_coherent(dev) &&
> > +	     !(attrs & (DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_MMIO))))
> 
> This isn't needed, since there's no way an MMIO mapping could have used
> SWIOTLB.

This "if" is taken even for non-SWIOTLB path, because of "||" operator
in line above.

Thanks

> 
> Thanks,
> Robin.
> 
> >   		iommu_dma_iova_unlink_range_slow(dev, addr, size, dir, attrs);
> >   	iommu_iotlb_gather_init(&iotlb_gather);
>