linux-kernel - Re: [PATCH v2 4/4] hugetlb/userfaultfd: Unshare all pmds for hugetlbfs when register wp

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Date:   Thu, 18 Feb 2021 12:34:55 -0800
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 4/4] hugetlb/userfaultfd: Unshare all pmds for
 hugetlbfs when register wp

On Thu, Feb 18, 2021 at 12:32 PM Peter Xu <peterx@...hat.com> wrote:
>
> On Thu, Feb 18, 2021 at 10:32:00AM -0800, Axel Rasmussen wrote:
> > > @@ -1448,6 +1449,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> > >                 vma->vm_flags = new_flags;
> > >                 vma->vm_userfaultfd_ctx.ctx = ctx;
> > >
> > > +               if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
> > > +                       hugetlb_unshare_all_pmds(vma);
> >
> > This line yields the following error, if building with:
> > # CONFIG_CMA is not set
> >
> > ./fs/userfaultfd.c:1459: undefined reference to `hugetlb_unshare_all_pmds'
>
> Ouch..  Axel, you mean CONFIG_HUGETLBFS rather than CONFIG_CMA, am I right?

Surprisingly no, there's a "#ifdef CONFIG_CMA" line ~100 lines above
where hugetlb_unshare_all_pmds is defined in hugetlb.c which causes
this. My guess is that putting the function inside that block was
accidental and it can just be moved.

>
> --
> Peter Xu
>