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    SubjectRe: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned
    On Wed, 3 Mar 2021 15:41:35 +0000
    "Luck, Tony" <tony.luck@intel.com> wrote:

    > > For error address with sigbus, i think this is not an issue resulted by the patch i post, before my patch, the issue is already there.
    > > I don't find a realizable way to get the correct address for same reason --- we don't know whether the page mapping is there or not when
    > > we got to kill_me_maybe(), in some case, we may get it, but there are a lot of parallel issue need to consider, and if failed we have to fallback
    > > to the error brach again, remaining current code may be an easy option;
    >
    > My RFC patch from yesterday removes the uncertainty about whether the page is there or not. After it walks the page
    > tables we know that the poison page isn't mapped (note that patch is RFC for a reason ... I'm 90% sure that it should
    > do a bit more that just clear the PRESENT bit).
    >
    > So perhaps memory_failure() has queued a SIGBUS for this task, if so, we take it when we return from kill_me_maybe()
    >
    > If not, we will return to user mode and re-execute the failing instruction ... but because the page is unmapped we will take a #PF

    Got this, I have some error thoughts here.


    > The x86 page fault handler will see that the page for this physical address is marked HWPOISON, and it will send the SIGBUS
    > (just like it does if the page had been removed by an earlier UCNA/SRAO error).

    if your methods works, should it be like this?

    1582 pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
    1583 if (PageHuge(page)) {
    1584 hugetlb_count_sub(compound_nr(page), mm);
    1585 set_huge_swap_pte_at(mm, address,
    1586 pvmw.pte, pteval,
    1587 vma_mmu_pagesize(vma));
    1588 } else {
    1589 dec_mm_counter(mm, mm_counter(page));
    1590 set_pte_at(mm, address, pvmw.pte, pteval);
    1591 }

    the page fault check if it's a poison page using is_hwpoison_entry(),

    --
    Thanks!
    Aili Yao

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