Peter Xu peterx@redhat.com 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