On Thu, Aug 18, 2022 at 02:34:45PM +0800, Huang, Ying wrote:

quoted

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