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This then causes Weird Stuff to > happen (for example an UBSAN splat in VT-d) that is hopefully harmless, > but maybe not. > > Prevent drivers from being called right in iommu_iotlb_sync(). > > Auditing shows that AMD, Intel, Mediatek and RSIC-V drivers all do things > on these empty gathers. > > Further, there are several callers that can trigger empty gathers, > especially in unusual conditions. For example iommu_map_nosync() will call > a 0 size unmap on some error paths. Also in VFIO, iommupt and other > places. > > Cc: stable@vger.kernel.org > Reported-by: Janusz Krzysztofik > Closes: https://lore.kernel.org/r/11145826.aFP6jjVeTY@jkrzyszt-mobl2.ger.corp.intel.com > Signed-off-by: Jason Gunthorpe > --- > include/linux/iommu.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > index 54b8b48c762e88..555597b54083cd 100644 > --- a/include/linux/iommu.h > +++ b/include/linux/iommu.h > @@ -980,7 +980,8 @@ static inline void iommu_flush_iotlb_all(struct iommu_domain *domain) > static inline void iommu_iotlb_sync(struct iommu_domain *domain, > struct iommu_iotlb_gather *iotlb_gather) > { > - if (domain->ops->iotlb_sync) > + if (domain->ops->iotlb_sync && > + likely(iotlb_gather->start < iotlb_gather->end)) > domain->ops->iotlb_sync(domain, iotlb_gather); > > iommu_iotlb_gather_init(iotlb_gather); I noticed that a couple of our Tegra boards are no longer booting -next and bisect pointed to this commit. Reverting this does fix it. This is impacting our Tegra186 (using nvidia,tegra186-smmu compatible string) and Tegra194 (using nvidia,tegra194-smmu compatible string) boards. There is no specific crash I see, but the boards just appear to hang on boot. If you have any thoughts or things to try let me know. Thanks! Jon -- nvpublic