Peter Xu <peterx@xxxxxxxxxx> writes: > 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? As you have said below, we don't use non-present PTEs and flush present PTEs before we access the pages. >> 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. Yes. I think so too. > 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. I don't think it's a good idea to be redundant. That may hide the real issue. Best Regards, Huang, Ying
