On 2/10/23 12:26 AM, Peter Xu wrote:
On Thu, Feb 02, 2023 at 04:29:14PM +0500, Muhammad Usama Anjum wrote:
Add some explanation and method to use write-protection and written-to on memory range.
Signed-off-by: Muhammad Usama Anjum usama.anjum@collabora.com
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``)
Could we extend this section a bit more? Some points for reference:
The new struct you introduced, definitions of each of the fields, and generic use cases for each of the field/ops.
It'll be nice to list the OPs the new interface supports (GET, WP_ENGAGE, GET+WP_ENGAGE).
When should people use this rather than the old pagemap interface? What's the major problems to solve / what's the major difference? (Maybe nice to reference the Windows API too here)
I'll update the documentation.
+To get information about which pages have been written-to and/or write protect +the pages, following must be performed first in order:
- The userfaultfd file descriptor is created with ``userfaultfd`` syscall.
- The ``UFFD_FEATURE_WP_ASYNC`` feature is set by ``UFFDIO_API`` IOCTL.
- 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.
This part looks good.
Thanks,