Re: [PATCH] iommu: Ensure .iotlb_sync is called correctly

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Wed, Apr 08, 2026 at 06:28:55PM +0100, Jon Hunter wrote:
> 
> On 08/04/2026 15:40, Robin Murphy wrote:
> > Many drivers have no reason to use the iotlb_gather mechanism, but do
> > still depend on .iotlb_sync being called to properly complete an unmap.
> > Since the core code is now relying on the gather to detect when there
> > is legitimately something to sync, it should also take care of encoding
> > a successful unmap when the driver does not touch the gather itself.
> > 
> > Fixes: 90c5def10bea ("iommu: Do not call drivers for empty gathers")
> > Reported-by: Jon Hunter <jonathanh@nvidia.com>
> > Closes: https://lore.kernel.org/r/8800a38b-8515-4bbe-af15-0dae81274bf7@nvidia.com
> > Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> > ---
> >   drivers/iommu/iommu.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 50718ab810a4..ee83850c7060 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -2717,6 +2717,12 @@ static size_t __iommu_unmap(struct iommu_domain *domain,
> >   		pr_debug("unmapped: iova 0x%lx size 0x%zx\n",
> >   			 iova, unmapped_page);
> > +		/*
> > +		 * If the driver itself isn't using the gather, make sure
> > +		 * it looks non-empty so iotlb_sync will still be called.
> > +		 */
> > +		if (iotlb_gather->start >= iotlb_gather->end)
> > +			iommu_iotlb_gather_add_range(iotlb_gather, iova, size);
> >   		iova += unmapped_page;
> >   		unmapped += unmapped_page;
> 
> 
> Tested-by: Jon Hunter <jonathanh@nvidia.com>

Tested-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

I think the commit message needs to spell out that the blamed commit
causes random memory corruption which leads to data corruption and
kernel oopses.

Thanks!

-- 
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