Re: [PATCH] iommu/dma: add missing support for DMA_ATTR_MMIO for dma_iova_unlink()

[Leon Romanovsky <leon@kernel.org>]

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@samsung.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);
>