Re: [PATCH 2/7] mm: introduce local state for lazy_mmu sections

[Kevin Brodsky]

On 04/09/2025 17:06, Yeoreum Yun wrote:
> Hi Kevin,
>
> [...]
>> Signed-off-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
>> ---
>>  arch/arm64/include/asm/pgtable.h              | 10 +++++++---
>>  .../include/asm/book3s/64/tlbflush-hash.h     |  9 ++++++---
>>  arch/powerpc/mm/book3s64/hash_tlb.c           | 10 ++++++----
>>  arch/powerpc/mm/book3s64/subpage_prot.c       |  5 +++--
>>  arch/sparc/include/asm/tlbflush_64.h          |  5 +++--
>>  arch/sparc/mm/tlb.c                           |  6 ++++--
>>  arch/x86/include/asm/paravirt.h               |  6 ++++--
>>  arch/x86/include/asm/paravirt_types.h         |  2 ++
>>  arch/x86/xen/enlighten_pv.c                   |  2 +-
>>  arch/x86/xen/mmu_pv.c                         |  2 +-
>>  fs/proc/task_mmu.c                            |  5 +++--
>>  include/linux/mm_types.h                      |  3 +++
>>  include/linux/pgtable.h                       |  6 ++++--
>>  mm/madvise.c                                  | 20 ++++++++++---------
>>  mm/memory.c                                   | 20 +++++++++++--------
>>  mm/migrate_device.c                           |  5 +++--
>>  mm/mprotect.c                                 |  5 +++--
>>  mm/mremap.c                                   |  5 +++--
>>  mm/vmalloc.c                                  | 15 ++++++++------
>>  mm/vmscan.c                                   | 15 ++++++++------
>>  20 files changed, 97 insertions(+), 59 deletions(-)
> I think you miss the mm/kasan/shadow.c

Ah yes that's because my series is based on v6.17-rc4 but [1] isn't in
mainline yet. I'll rebase v2 on top of mm-stable.

[1]
https://lore.kernel.org/all/0d2efb7ddddbff6b288fbffeeb10166e90771718.1755528662.git.agordeev@xxxxxxxxxxxxx/

> But here, the usage is like:
>
> static int kasan_populate_vmalloc_pte()
> {
> 	...
> 	arch_leave_lazy_mmu_mode();
> 	...
> 	arch_enter_lazy_mmu_mode();
> 	...
> }
>
> Might be you can call the arch_leave_lazy_mmu_mode() with LAZY_MMU_DEFAULT
> in here since I think kasan_populate_vmalloc_pte() wouldn't be called
> nestly.

In fact in that case it doesn't matter if the section is nested or not.
We're already assuming that lazy_mmu is enabled, and we want to fully
disable it so that PTE operations take effect immediately. For that to
happen we must call arch_leave_lazy_mmu_mode(LAZY_MMU_DEFAULT). We will
then re-enable lazy_mmu, and the next call to leave() will do the right
thing whether it is nested or not.

It's worth nothing the same situation occurs in xen_flush_lazy_mmu() and
this patch handles it in the way I've just described.

I'll take care of that in v2, thanks for the heads-up!

- Kevin