Add some explanation and method to use write-protection and written-to on memory range. Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx> --- Documentation/admin-guide/mm/pagemap.rst | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst index 6e2e416af783..1cb2189e9a0d 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -230,3 +230,27 @@ Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is always 12 at most architectures). Since Linux 3.11 their meaning changes after first clear of soft-dirty bits. Since Linux 4.2 they are used for flags unconditionally. + +Pagemap Scan IOCTL +================== + +The ``PAGEMAP_SCAN`` IOCTL on the pagemap file can be used to get and/or clear +the info about page table entries. The following operations are supported in +this IOCTL: +- Get the information if the pages have been written-to (``PAGE_IS_WRITTEN``), + file mapped (``PAGE_IS_FILE``), present (``PAGE_IS_PRESENT``) or swapped + (``PAGE_IS_SWAPPED``). +- Write-protect the pages (``PAGEMAP_WP_ENGAGE``) to start finding which + pages have been written-to. +- Find pages which have been written-to and write protect the pages + (atomic ``PAGE_IS_WRITTEN + PAGEMAP_WP_ENGAGE``) + +To get information about which pages have been written-to and/or write protect +the pages, following must be performed first in order: + 1. The userfaultfd file descriptor is created with ``userfaultfd`` syscall. + 2. The ``UFFD_FEATURE_WP_ASYNC`` feature is set by ``UFFDIO_API`` IOCTL. + 3. The memory range is registered with ``UFFDIO_REGISTER_MODE_WP`` mode + through ``UFFDIO_REGISTER`` IOCTL. +Then the any part of the registered memory or the whole memory region can be +write protected using the ``UFFDIO_WRITEPROTECT`` IOCTL or ``PAGEMAP_SCAN`` +IOCTL. -- 2.30.2
