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SubjectRe: [v3 PATCH] mm: mmu_gather: remove __tlb_reset_range() for force flush
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On 5/22/19 7:18 AM, Andrew Morton wrote:
> On Mon, 20 May 2019 11:17:32 +0800 Yang Shi <yang.shi@linux.alibaba.com> wrote:
>
>> A few new fields were added to mmu_gather to make TLB flush smarter for
>> huge page by telling what level of page table is changed.
>>
>> __tlb_reset_range() is used to reset all these page table state to
>> unchanged, which is called by TLB flush for parallel mapping changes for
>> the same range under non-exclusive lock (i.e. read mmap_sem). Before
>> commit dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in
>> munmap"), the syscalls (e.g. MADV_DONTNEED, MADV_FREE) which may update
>> PTEs in parallel don't remove page tables. But, the forementioned
>> commit may do munmap() under read mmap_sem and free page tables. This
>> may result in program hang on aarch64 reported by Jan Stancek. The
>> problem could be reproduced by his test program with slightly modified
>> below.
>>
>> ...
>>
>> Use fullmm flush since it yields much better performance on aarch64 and
>> non-fullmm doesn't yields significant difference on x86.
>>
>> The original proposed fix came from Jan Stancek who mainly debugged this
>> issue, I just wrapped up everything together.
> Thanks. I'll add
>
> Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap")
>
> to this.

Thanks, Andrew.


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