Re: [PATCH 3/3] mm:fix gup_pud_range

[黄秋钧 <hqjagain@gmail.com>]

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>On Fri, Sep 20, 2019 at 11:58 PM Aneesh Kumar K.V <
aneesh.kumar@linux.ibm.com> wrote:

> >On 9/20/19 9:21 PM, Qiujun Huang wrote:
> >> __get_user_pages_fast try to walk the page table but the
> > >hugepage pte is replace by hwpoison swap entry by mca path.
> > >...
> >
> >

 >Can you describe this in more details. I guess you are facing the issue

> >with respect PUD level PTE entry that got updated by hwpoison as a swap
> >entry. Since we don't specifically check for pud_present(), we walk the
> >page table with wrong values and that results in corruption?
>

Yes, in the case using 2G hugepage.

>
>
> >> [15798.177437] mce: Uncorrected hardware memory error in
> >>                               user-access at 224f1761c0
> > >[15798.180171] MCE 0x224f176: Killing pal_main:6784 due to
> > >                              hardware memory corruption
> > >[15798.180176] MCE 0x224f176: Killing qemu-system-x86:167336
> > >                             due to hardware memory corruption
> >> ...
> >> [15798.180206] BUG: unable to handle kernel
> >> [15798.180226] paging request at ffff891200003000
> >> [15798.180236] IP: [<ffffffff8106edae>] gup_pud_range+
> >>                               0x13e/0x1e0
> >> ...
> >>
> >> We need to skip the hwpoison entry in gup_pud_range.
> >>
> >> Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
> >> ---
> >>   mm/gup.c | 2 ++
> >>   1 file changed, 2 insertions(+)
> >>
> >> diff --git a/mm/gup.c b/mm/gup.c
> >> index 98f13ab..6157ed9 100644
> >> --- a/mm/gup.c
> >> +++ b/mm/gup.c
> >> @@ -2230,6 +2230,8 @@ static int gup_pud_range(p4d_t p4d, unsigned long
> addr, unsigned long end,
> >>               next = pud_addr_end(addr, end);
> >>               if (pud_none(pud))
> >>                       return 0;
> >> +             if (unlikely(!pud_present(pud)))
> >> +                     return 0;
>
>
>You should be able to remove that if (pud_none(pud)) check and just keep
> >the pud_present() check?
>
 indeed

>
> >>               if (unlikely(pud_huge(pud))) {
> >>                       if (!gup_huge_pud(pud, pudp, addr, next, flags,
> >>                                         pages, nr))
> >>
>
>
diff --git a/mm/gup.c b/mm/gup.c
index 98f13ab..2e3a1d3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2228,7 +2228,7 @@ static int gup_pud_range(p4d_t p4d, unsigned long
addr, unsigned long end,
                pud_t pud = READ_ONCE(*pudp);
                next = pud_addr_end(addr, end);
-               if (pud_none(pud))
+              if (!pud_present(pud))
                        return 0;
                if (unlikely(pud_huge(pud))) {
                        if (!gup_huge_pud(pud, pudp, addr, next, flags,

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