From: Mike Rapoport <rppt@linux.ibm.com>
To: Peter Xu <peterx@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
David Hildenbrand <david@redhat.com>,
Hugh Dickins <hughd@google.com>, Maya Gokhale <gokhale2@llnl.gov>,
Jerome Glisse <jglisse@redhat.com>,
Pavel Emelyanov <xemul@virtuozzo.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Martin Cracauer <cracauer@cons.org>, Shaohua Li <shli@fb.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Denis Plotnikov <dplotnikov@virtuozzo.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Marty McFadden <mcfadden8@llnl.gov>, Mel Gorman <mgorman@suse.de>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: [PATCH v3 24/28] userfaultfd: wp: UFFDIO_REGISTER_MODE_WP documentation update
Date: Fri, 22 Mar 2019 23:46:20 +0200 [thread overview]
Message-ID: <20190322214620.GD9303@rapoport-lnx> (raw)
In-Reply-To: <20190320020642.4000-25-peterx@redhat.com>
On Wed, Mar 20, 2019 at 10:06:38AM +0800, Peter Xu wrote:
> From: Martin Cracauer <cracauer@cons.org>
>
> Adds documentation about the write protection support.
>
> Signed-off-by: Martin Cracauer <cracauer@cons.org>
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> [peterx: rewrite in rst format; fixups here and there]
> Reviewed-by: Jerome Glisse <jglisse@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
> Documentation/admin-guide/mm/userfaultfd.rst | 51 ++++++++++++++++++++
> 1 file changed, 51 insertions(+)
>
> diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
> index 5048cf661a8a..c30176e67900 100644
> --- a/Documentation/admin-guide/mm/userfaultfd.rst
> +++ b/Documentation/admin-guide/mm/userfaultfd.rst
> @@ -108,6 +108,57 @@ UFFDIO_COPY. They're atomic as in guaranteeing that nothing can see an
> half copied page since it'll keep userfaulting until the copy has
> finished.
>
> +Notes:
> +
> +- If you requested UFFDIO_REGISTER_MODE_MISSING when registering then
> + you must provide some kind of page in your thread after reading from
> + the uffd. You must provide either UFFDIO_COPY or UFFDIO_ZEROPAGE.
> + The normal behavior of the OS automatically providing a zero page on
> + an annonymous mmaping is not in place.
> +
> +- None of the page-delivering ioctls default to the range that you
> + registered with. You must fill in all fields for the appropriate
> + ioctl struct including the range.
> +
> +- You get the address of the access that triggered the missing page
> + event out of a struct uffd_msg that you read in the thread from the
> + uffd. You can supply as many pages as you want with UFFDIO_COPY or
> + UFFDIO_ZEROPAGE. Keep in mind that unless you used DONTWAKE then
> + the first of any of those IOCTLs wakes up the faulting thread.
> +
> +- Be sure to test for all errors including (pollfd[0].revents &
> + POLLERR). This can happen, e.g. when ranges supplied were
> + incorrect.
> +
> +Write Protect Notifications
> +---------------------------
> +
> +This is equivalent to (but faster than) using mprotect and a SIGSEGV
> +signal handler.
> +
> +Firstly you need to register a range with UFFDIO_REGISTER_MODE_WP.
> +Instead of using mprotect(2) you use ioctl(uffd, UFFDIO_WRITEPROTECT,
> +struct *uffdio_writeprotect) while mode = UFFDIO_WRITEPROTECT_MODE_WP
> +in the struct passed in. The range does not default to and does not
> +have to be identical to the range you registered with. You can write
> +protect as many ranges as you like (inside the registered range).
> +Then, in the thread reading from uffd the struct will have
> +msg.arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WP set. Now you send
> +ioctl(uffd, UFFDIO_WRITEPROTECT, struct *uffdio_writeprotect) again
> +while pagefault.mode does not have UFFDIO_WRITEPROTECT_MODE_WP set.
> +This wakes up the thread which will continue to run with writes. This
> +allows you to do the bookkeeping about the write in the uffd reading
> +thread before the ioctl.
> +
> +If you registered with both UFFDIO_REGISTER_MODE_MISSING and
> +UFFDIO_REGISTER_MODE_WP then you need to think about the sequence in
> +which you supply a page and undo write protect. Note that there is a
> +difference between writes into a WP area and into a !WP area. The
> +former will have UFFD_PAGEFAULT_FLAG_WP set, the latter
> +UFFD_PAGEFAULT_FLAG_WRITE. The latter did not fail on protection but
> +you still need to supply a page when UFFDIO_REGISTER_MODE_MISSING was
> +used.
> +
> QEMU/KVM
> ========
>
> --
> 2.17.1
>
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2019-03-22 21:46 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-20 2:06 [PATCH v3 00/28] userfaultfd: write protection support Peter Xu
2019-03-20 2:06 ` [PATCH v3 01/28] mm: gup: rename "nonblocking" to "locked" where proper Peter Xu
2019-03-20 2:06 ` [PATCH v3 02/28] mm: userfault: return VM_FAULT_RETRY on signals Peter Xu
2019-03-20 2:06 ` [PATCH v3 03/28] userfaultfd: don't retake mmap_sem to emulate NOPAGE Peter Xu
2019-03-20 2:06 ` [PATCH v3 04/28] mm: allow VM_FAULT_RETRY for multiple times Peter Xu
2019-04-18 20:11 ` Jerome Glisse
2019-04-19 6:00 ` Peter Xu
2019-03-20 2:06 ` [PATCH v3 05/28] mm: gup: " Peter Xu
2019-03-20 2:06 ` [PATCH v3 06/28] userfaultfd: wp: add helper for writeprotect check Peter Xu
2019-03-20 2:06 ` [PATCH v3 07/28] userfaultfd: wp: hook userfault handler to write protection fault Peter Xu
2019-04-18 20:03 ` Jerome Glisse
2019-03-20 2:06 ` [PATCH v3 08/28] userfaultfd: wp: add WP pagetable tracking to x86 Peter Xu
2019-03-20 2:06 ` [PATCH v3 09/28] userfaultfd: wp: userfaultfd_pte/huge_pmd_wp() helpers Peter Xu
2019-03-20 2:06 ` [PATCH v3 10/28] userfaultfd: wp: add UFFDIO_COPY_MODE_WP Peter Xu
2019-03-20 2:06 ` [PATCH v3 11/28] mm: merge parameters for change_protection() Peter Xu
2019-03-20 2:06 ` [PATCH v3 12/28] userfaultfd: wp: apply _PAGE_UFFD_WP bit Peter Xu
2019-03-20 2:06 ` [PATCH v3 13/28] mm: export wp_page_copy() Peter Xu
2019-03-20 2:06 ` [PATCH v3 14/28] userfaultfd: wp: handle COW properly for uffd-wp Peter Xu
2019-04-18 20:51 ` Jerome Glisse
2019-04-19 6:26 ` Peter Xu
2019-04-19 15:02 ` Jerome Glisse
2019-04-22 12:20 ` Peter Xu
2019-04-22 14:54 ` Jerome Glisse
2019-04-23 3:00 ` Peter Xu
2019-04-23 15:34 ` Jerome Glisse
2019-04-24 8:38 ` Peter Xu
2019-03-20 2:06 ` [PATCH v3 15/28] userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork Peter Xu
2019-03-20 2:06 ` [PATCH v3 16/28] userfaultfd: wp: add pmd_swp_*uffd_wp() helpers Peter Xu
2019-03-20 2:06 ` [PATCH v3 17/28] userfaultfd: wp: support swap and page migration Peter Xu
2019-04-18 20:59 ` Jerome Glisse
2019-04-19 7:42 ` Peter Xu
2019-04-19 15:08 ` Jerome Glisse
2019-04-22 12:23 ` Peter Xu
2019-03-20 2:06 ` [PATCH v3 18/28] khugepaged: skip collapse if uffd-wp detected Peter Xu
2019-03-20 2:06 ` [PATCH v3 19/28] userfaultfd: introduce helper vma_find_uffd Peter Xu
2019-03-20 2:06 ` [PATCH v3 20/28] userfaultfd: wp: support write protection for userfault vma range Peter Xu
2019-03-20 2:06 ` [PATCH v3 21/28] userfaultfd: wp: add the writeprotect API to userfaultfd ioctl Peter Xu
2019-03-20 2:06 ` [PATCH v3 22/28] userfaultfd: wp: enabled write protection in userfaultfd API Peter Xu
2019-03-22 21:37 ` Mike Rapoport
2019-03-20 2:06 ` [PATCH v3 23/28] userfaultfd: wp: don't wake up when doing write protect Peter Xu
2019-03-20 2:06 ` [PATCH v3 24/28] userfaultfd: wp: UFFDIO_REGISTER_MODE_WP documentation update Peter Xu
2019-03-22 21:46 ` Mike Rapoport [this message]
2019-03-20 2:06 ` [PATCH v3 25/28] userfaultfd: wp: fixup swap entries in change_pte_range Peter Xu
2019-04-18 21:01 ` Jerome Glisse
2019-03-20 2:06 ` [PATCH v3 26/28] userfaultfd: wp: declare _UFFDIO_WRITEPROTECT conditionally Peter Xu
2019-03-22 21:43 ` Mike Rapoport
2019-03-20 2:06 ` [PATCH v3 27/28] userfaultfd: selftests: refactor statistics Peter Xu
2019-03-20 2:06 ` [PATCH v3 28/28] userfaultfd: selftests: add write-protect test Peter Xu
2019-04-09 6:08 ` [PATCH v3 00/28] userfaultfd: write protection support Peter Xu
2019-04-18 21:07 ` Jerome Glisse
2019-04-19 7:53 ` Peter Xu
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