On Tue, 18 Jul 2023 17:56:17 +1000 Alistair Popple <apopple@xxxxxxxxxx> wrote: > The arch_invalidate_secondary_tlbs() is an architecture specific mmu > notifier used to keep the TLB of secondary MMUs such as an IOMMU in > sync with the CPU page tables. Currently it is called from separate > code paths to the main CPU TLB invalidations. This can lead to a > secondary TLB not getting invalidated when required and makes it hard > to reason about when exactly the secondary TLB is invalidated. > > To fix this move the notifier call to the architecture specific TLB > maintenance functions for architectures that have secondary MMUs > requiring explicit software invalidations. > > This fixes a SMMU bug on ARM64. On ARM64 PTE permission upgrades > require a TLB invalidation. This invalidation is done by the > architecutre specific ptep_set_access_flags() which calls > flush_tlb_page() if required. However this doesn't call the notifier > resulting in infinite faults being generated by devices using the SMMU > if it has previously cached a read-only PTE in it's TLB. This sounds like a pretty serious bug. Can it happen in current released kernels? If so, is a -stable backport needed? > Moving the invalidations into the TLB invalidation functions ensures > all invalidations happen at the same time as the CPU invalidation. The > architecture specific flush_tlb_all() routines do not call the > notifier as none of the IOMMUs require this.
