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Miller" , Andreas Larsson , Juergen Gross , Ajay Kaher , Alexey Makhalov , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Boris Ostrovsky , "Aneesh Kumar K.V" , Andrew Morton , Peter Zijlstra , Arnd Bergmann , David Hildenbrand , "Liam R. 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owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: +cc Jann who is a specialist in all things page table-y and especially scary edge cases :) On Fri, May 30, 2025 at 03:04:38PM +0100, Ryan Roberts wrote: > Hi All, > > I recently added support for lazy mmu mode on arm64. The series is now in > Linus's tree so should be in v6.16-rc1. But during testing in linux-next we > found some ugly corners (unexpected nesting). I was able to fix those issues by > making the arm64 implementation more permissive (like the other arches). But > this is quite fragile IMHO. So I'd rather fix the root cause and ensure that > lazy mmu mode never nests, and more importantly, that code never makes pgtable > modifications expecting them to be immediate, not knowing that it's actually in > lazy mmu mode so the changes get deferred. When you say fragile, are you confident it _works_ but perhaps not quite as well as you want? Or are you concerned this might be broken upstream in any way? I am thinking specifically about the proposed use in Dev's new series [0] and obviously hoping (and assuming in fact) that it's the former :) [0]: https://lore.kernel.org/linux-mm/20250530090407.19237-1-dev.jain@arm.com/ > > The first 2 patches are unrelated, very obvious bug fixes. They don't affect > arm64 because arm64 only uses lazy mmu for kernel mappings. But I noticed them > during code review and think they should be fixed. > > The next 3 patches are aimed at solving the nesting issue. > > And the final patch is reverting the "permissive" fix I did for arm64, which is > no longer needed after the previous 3 patches. > > I've labelled this RFC for now because it depends on the arm64 lazy mmu patches > in Linus's master, so it won't apply to mm-unstable. But I'm keen to get review > and siince I'm touching various arches and modifying some core mm stuff, I > thought that might take a while so thought I'd beat the rush and get a first > version out early. > > I've build-tested all the affected arches. And I've run mm selftests for the > arm64 build, with no issues (with DEBUG_PAGEALLOC and KFENCE enabled). > > Applies against Linus's master branch (f66bc387efbe). > > Thanks, > Ryan > > > Ryan Roberts (6): > fs/proc/task_mmu: Fix pte update and tlb maintenance ordering in > pagemap_scan_pmd_entry() > mm: Fix pte update and tlb maintenance ordering in > migrate_vma_collect_pmd() > mm: Avoid calling page allocator from apply_to_page_range() > mm: Introduce arch_in_lazy_mmu_mode() > mm: Avoid calling page allocator while in lazy mmu mode > Revert "arm64/mm: Permit lazy_mmu_mode to be nested" > > arch/arm64/include/asm/pgtable.h | 22 ++++---- > .../include/asm/book3s/64/tlbflush-hash.h | 15 ++++++ > arch/sparc/include/asm/tlbflush_64.h | 1 + > arch/sparc/mm/tlb.c | 12 +++++ > arch/x86/include/asm/paravirt.h | 5 ++ > arch/x86/include/asm/paravirt_types.h | 1 + > arch/x86/kernel/paravirt.c | 6 +++ > arch/x86/xen/mmu_pv.c | 6 +++ > fs/proc/task_mmu.c | 3 +- > include/asm-generic/tlb.h | 2 + > include/linux/mm.h | 6 +++ > include/linux/pgtable.h | 1 + > kernel/bpf/arena.c | 6 +-- > mm/kasan/shadow.c | 2 +- > mm/memory.c | 54 ++++++++++++++----- > mm/migrate_device.c | 3 +- > mm/mmu_gather.c | 15 ++++++ > 17 files changed, 128 insertions(+), 32 deletions(-) > > -- > 2.43.0 >