Messages in this thread | | | Date | Thu, 18 Aug 2022 10:44:46 -0400 | From | Peter Xu <> | Subject | Re: [PATCH v2 1/2] mm/migrate_device.c: Copy pte dirty bit to page |
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On Thu, Aug 18, 2022 at 02:34:45PM +0800, Huang, Ying wrote: > > In this specific case, the only way to do safe tlb batching in my mind is: > > > > pte_offset_map_lock(); > > arch_enter_lazy_mmu_mode(); > > // If any pending tlb, do it now > > if (mm_tlb_flush_pending()) > > flush_tlb_range(vma, start, end); > > else > > flush_tlb_batched_pending(); > > I don't think we need the above 4 lines. Because we will flush TLB > before we access the pages.
Could you elaborate?
> Can you find any issue if we don't use the above 4 lines?
It seems okay to me to leave stall tlb at least within the scope of this function. It only collects present ptes and flush propoerly for them. I don't quickly see any other implications to other not touched ptes - unlike e.g. mprotect(), there's a strong barrier of not allowing further write after mprotect() returns.
Still I don't know whether there'll be any side effect of having stall tlbs in !present ptes because I'm not familiar enough with the private dev swap migration code. But I think having them will be safe, even if redundant.
Thanks,
-- Peter Xu
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