On Fri, 26 May 2023, Peter Xu wrote: > > The other confusing thing on this _lockless trick on PAE is, I think it > _might_ go wrong with devmap.. > > The problem is here we assumed even if high & low may not match, we still > can rely on most pte/pmd checks are done only on low bits (except _none() > check) to guarantee at least the checks are still atomic on low bits. > > But it seems to me it's not true anymore if with pmd_trans_huge() after > devmap introduced, e.g.: I agree that there would likely be a problem for p??_devmap() on 32-bit PAE: but (I hope I followed the chain correctly!) I had earlier found that pmd_devmap() can only return true when CONFIG_ZONE_DEVICE=y, and config ZONE_DEVICE depends on ARCH_HAS_PTE_DEVMAP, and ARCH_HAS_PTE_DEVMAP is only selected (in some cases) by arm64, powerpc if PPC_BOOK3S_64, and x86 if X86_64. So I stopped worrying about devmap. Hugh
