From: Naresh Kamboju <naresh.kamboju@linaro.org>
To: Peter Xu <peterx@redhat.com>
Cc: Linux-Next Mailing List <linux-next@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Axel Rasmussen <axelrasmussen@google.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
Andrew Morton <akpm@linux-foundation.org>,
Matthew Wilcox <willy@infradead.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
lkft-triage@lists.linaro.org, Arnd Bergmann <arnd@arndb.de>,
Stephen Rothwell <sfr@canb.auug.org.au>
Subject: Re: [PATCH v4 2/4] hugetlb/userfaultfd: Forbid huge pmd sharing when uffd enabled
Date: Wed, 10 Mar 2021 23:39:32 +0530 [thread overview]
Message-ID: <CA+G9fYs7wZ7EfOs1eB=2zf94=pYEkWig=usYF=Hfs5sM6iqYKw@mail.gmail.com> (raw)
In-Reply-To: <20210310165713.GB6530@xz-x1>
On Wed, 10 Mar 2021 at 22:27, Peter Xu <peterx@redhat.com> wrote:
>
> On Wed, Mar 10, 2021 at 01:18:42PM +0530, Naresh Kamboju wrote:
> > Hi Peter,
>
> Hi, Naresh,
>
> >
> > On Fri, 19 Feb 2021 at 04:43, Peter Xu <peterx@redhat.com> wrote:
> > >
> > > Huge pmd sharing could bring problem to userfaultfd. The thing is that
> > > userfaultfd is running its logic based on the special bits on page table
> > > entries, however the huge pmd sharing could potentially share page table
> > > entries for different address ranges. That could cause issues on either:
> > >
> > > - When sharing huge pmd page tables for an uffd write protected range, the
> > > newly mapped huge pmd range will also be write protected unexpectedly, or,
> > >
> > > - When we try to write protect a range of huge pmd shared range, we'll first
> > > do huge_pmd_unshare() in hugetlb_change_protection(), however that also
> > > means the UFFDIO_WRITEPROTECT could be silently skipped for the shared
> > > region, which could lead to data loss.
> > >
> > > Since at it, a few other things are done altogether:
> > >
> > > - Move want_pmd_share() from mm/hugetlb.c into linux/hugetlb.h, because
> > > that's definitely something that arch code would like to use too
> > >
> > > - ARM64 currently directly check against CONFIG_ARCH_WANT_HUGE_PMD_SHARE when
> > > trying to share huge pmd. Switch to the want_pmd_share() helper.
> > >
> > > Since at it, move vma_shareable() from huge_pmd_share() into want_pmd_share().
> > >
> > > Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> > > Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
> > > Signed-off-by: Peter Xu <peterx@redhat.com>
> > > ---
> > > arch/arm64/mm/hugetlbpage.c | 3 +--
> > > include/linux/hugetlb.h | 2 ++
> > > include/linux/userfaultfd_k.h | 9 +++++++++
> > > mm/hugetlb.c | 20 ++++++++++++++------
> > > 4 files changed, 26 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> > > index 6e3bcffe2837..58987a98e179 100644
> > > --- a/arch/arm64/mm/hugetlbpage.c
> > > +++ b/arch/arm64/mm/hugetlbpage.c
> > > @@ -284,8 +284,7 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
> > > */
> > > ptep = pte_alloc_map(mm, pmdp, addr);
> > > } else if (sz == PMD_SIZE) {
> > > - if (IS_ENABLED(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) &&
> > > - pud_none(READ_ONCE(*pudp)))
> > > + if (want_pmd_share(vma, addr) && pud_none(READ_ONCE(*pudp)))
> >
> > While building Linux next 20210310 tag for arm64 architecture with
> >
> > - CONFIG_ARM64_64K_PAGES=y
> >
> > enabled the build failed due to below errors / warnings
> >
> > make --silent --keep-going --jobs=8
> > O=/home/tuxbuild/.cache/tuxmake/builds/1/tmp ARCH=arm64
> > CROSS_COMPILE=aarch64-linux-gnu- 'CC=sccache aarch64-linux-gnu-gcc'
> > 'HOSTCC=sccache gcc'
> > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected!
> > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected!
> > aarch64-linux-gnu-ld: arch/arm64/mm/hugetlbpage.o: in function `huge_pte_alloc':
> > hugetlbpage.c:(.text+0x7d8): undefined reference to `want_pmd_share'
> >
> > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
>
> Sorry for the issue & thanks for the report. Would you please check whether
> the patch attached could fix the issue?
The attached patch build tested and build pass for arm64
including 64k pages config.
CONFIG_ARM64_64K_PAGES=y
- Naresh
next prev parent reply other threads:[~2021-03-10 18:09 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-18 23:06 [PATCH v4 0/4] hugetlb: Disable huge pmd unshare for uffd-wp Peter Xu
2021-02-18 23:06 ` [PATCH v4 1/4] hugetlb: Pass vma into huge_pte_alloc() and huge_pmd_share() Peter Xu
2021-03-04 16:31 ` kernel test robot
2021-03-04 16:46 ` Peter Xu
2021-02-18 23:12 ` [PATCH v4 2/4] hugetlb/userfaultfd: Forbid huge pmd sharing when uffd enabled Peter Xu
2021-03-10 7:48 ` Naresh Kamboju
2021-03-10 16:57 ` Peter Xu
2021-03-10 18:09 ` Naresh Kamboju [this message]
2021-02-18 23:12 ` [PATCH v4 3/4] mm/hugetlb: Move flush_hugetlb_tlb_range() into hugetlb.h Peter Xu
2021-02-18 23:12 ` [PATCH v4 4/4] hugetlb/userfaultfd: Unshare all pmds for hugetlbfs when register wp Peter Xu
2021-03-01 14:20 ` [PATCH v4 0/4] hugetlb: Disable huge pmd unshare for uffd-wp Peter Xu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CA+G9fYs7wZ7EfOs1eB=2zf94=pYEkWig=usYF=Hfs5sM6iqYKw@mail.gmail.com' \
--to=naresh.kamboju@linaro.org \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=arnd@arndb.de \
--cc=axelrasmussen@google.com \
--cc=kirill@shutemov.name \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-next@vger.kernel.org \
--cc=lkft-triage@lists.linaro.org \
--cc=mike.kravetz@oracle.com \
--cc=peterx@redhat.com \
--cc=rppt@linux.vnet.ibm.com \
--cc=sfr@canb.auug.org.au \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).