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Date: Thu, 2 Feb 2023 16:29:14 +0500
From: Muhammad Usama Anjum <usama.anjum@...labora.com>
To: Peter Xu <peterx@...hat.com>, David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Michał Mirosław <emmir@...gle.com>,
Andrei Vagin <avagin@...il.com>,
Danylo Mocherniuk <mdanylo@...gle.com>,
Paul Gofman <pgofman@...eweavers.com>,
Cyrill Gorcunov <gorcunov@...il.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
Shuah Khan <shuah@...nel.org>,
Christian Brauner <brauner@...nel.org>,
Yang Shi <shy828301@...il.com>,
Vlastimil Babka <vbabka@...e.cz>,
"Liam R . Howlett" <Liam.Howlett@...cle.com>,
Yun Zhou <yun.zhou@...driver.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Alex Sierra <alex.sierra@....com>,
Muhammad Usama Anjum <usama.anjum@...labora.com>,
Matthew Wilcox <willy@...radead.org>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
"Gustavo A . R . Silva" <gustavoars@...nel.org>,
Dan Williams <dan.j.williams@...el.com>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
Greg KH <gregkh@...uxfoundation.org>, kernel@...labora.com
Subject: [PATCH v10 5/6] mm/pagemap: add documentation of PAGEMAP_SCAN IOCTL
Add some explanation and method to use write-protection and written-to
on memory range.
Signed-off-by: Muhammad Usama Anjum <usama.anjum@...labora.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``)
+
+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
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