The patch titled
Subject: mm: provide mapping_wrprotect_page() function
has been added to the -mm mm-unstable branch. Its filename is
mm-provide-mapping_wrprotect_page-function.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-provide-mapping_wrprotect_page-function.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Subject: mm: provide mapping_wrprotect_page() function
Date: Fri, 31 Jan 2025 18:28:57 +0000
In the fb_defio video driver, page dirty state is used to determine when
frame buffer pages have been changed, allowing for batched, deferred I/O
to be performed for efficiency.
This implementation had only one means of doing so effectively - the use
of the folio_mkclean() function.
However, this use of the function is inappropriate, as the fb_defio
implementation allocates kernel memory to back the framebuffer, and then
is forced to specified page->index, mapping fields in order to permit the
folio_mkclean() rmap traversal to proceed correctly.
It is not correct to specify these fields on kernel-allocated memory, and
moreover since these are not folios, page->index, mapping are deprecated
fields, soon to be removed.
We therefore need to provide a means by which we can correctly traverse
the reverse mapping and write-protect mappings for a page backing an
address_space page cache object at a given offset.
This patch provides this - mapping_wrprotect_page() allows for this
operation to be performed for a specified address_space, offset and page,
without requiring a folio nor, of course, an inappropriate use of
page->index, mapping.
With this provided, we can subequently adjust the fb_defio implementation
to make use of this function and avoid incorrect invocation of
folio_mkclean() and more importantly, incorrect manipulation of
page->index, mapping fields.
Link: https://lkml.kernel.org/r/c802c17cdba59e3455f3d7db07659d5da0ed6dc1.1738347308.git.lorenzo.stoakes@xxxxxxxxxx
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: Jaya Kumar <jayakumar.lkml@xxxxxxxxx>
Cc: Kajtar Zsolt <soci@xxxxxxxxxxxxx>
Cc: MaÃra Canal <mcanal@xxxxxxxxxx>
Cc: Mattew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/rmap.h | 3 +
mm/rmap.c | 73 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 76 insertions(+)
--- a/include/linux/rmap.h~mm-provide-mapping_wrprotect_page-function
+++ a/include/linux/rmap.h
@@ -739,6 +739,9 @@ unsigned long page_address_in_vma(const
*/
int folio_mkclean(struct folio *);
+int mapping_wrprotect_page(struct address_space *mapping, pgoff_t pgoff,
+ unsigned long nr_pages, struct page *page);
+
int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
struct vm_area_struct *vma);
--- a/mm/rmap.c~mm-provide-mapping_wrprotect_page-function
+++ a/mm/rmap.c
@@ -1129,6 +1129,79 @@ int folio_mkclean(struct folio *folio)
}
EXPORT_SYMBOL_GPL(folio_mkclean);
+struct wrprotect_file_state {
+ int cleaned;
+ pgoff_t pgoff;
+ unsigned long pfn;
+ unsigned long nr_pages;
+};
+
+static bool mapping_wrprotect_page_one(struct folio *folio,
+ struct vm_area_struct *vma, unsigned long address, void *arg)
+{
+ struct wrprotect_file_state *state = (struct wrprotect_file_state *)arg;
+ struct page_vma_mapped_walk pvmw = {
+ .pfn = state->pfn,
+ .nr_pages = state->nr_pages,
+ .pgoff = state->pgoff,
+ .vma = vma,
+ .address = address,
+ .flags = PVMW_SYNC,
+ };
+
+ state->cleaned += page_vma_mkclean_one(&pvmw);
+
+ return true;
+}
+
+static void __rmap_walk_file(struct folio *folio, struct address_space *mapping,
+ pgoff_t pgoff_start, unsigned long nr_pages,
+ struct rmap_walk_control *rwc, bool locked);
+
+/**
+ * mapping_wrprotect_page() - Write protect all mappings of this page.
+ *
+ * @mapping: The mapping whose reverse mapping should be traversed.
+ * @pgoff: The page offset at which @page is mapped within @mapping.
+ * @nr_pages: The number of physically contiguous base pages spanned.
+ * @page: The page mapped in @mapping at @pgoff.
+ *
+ * Traverses the reverse mapping, finding all VMAs which contain a shared
+ * mapping of the single @page in @mapping at offset @pgoff and write-protecting
+ * the mappings.
+ *
+ * The page does not have to be a folio, but rather can be a kernel allocation
+ * that is mapped into userland. We therefore do not require that the page maps
+ * to a folio with a valid mapping or index field, rather these are specified in
+ * @mapping and @pgoff.
+ *
+ * Return: the number of write-protected PTEs, or an error.
+ */
+int mapping_wrprotect_page(struct address_space *mapping, pgoff_t pgoff,
+ unsigned long nr_pages, struct page *page)
+{
+ struct wrprotect_file_state state = {
+ .cleaned = 0,
+ .pgoff = pgoff,
+ .pfn = page_to_pfn(page),
+ .nr_pages = nr_pages,
+ };
+ struct rmap_walk_control rwc = {
+ .arg = (void *)&state,
+ .rmap_one = mapping_wrprotect_page_one,
+ .invalid_vma = invalid_mkclean_vma,
+ };
+
+ if (!mapping)
+ return 0;
+
+ __rmap_walk_file(/* folio = */NULL, mapping, pgoff, nr_pages, &rwc,
+ /* locked = */false);
+
+ return state.cleaned;
+}
+EXPORT_SYMBOL_GPL(mapping_wrprotect_page);
+
/**
* pfn_mkclean_range - Cleans the PTEs (including PMDs) mapped with range of
* [@pfn, @pfn + @nr_pages) at the specific offset (@pgoff)
_
Patches currently in -mm which might be from lorenzo.stoakes@xxxxxxxxxx are
mm-simplify-vma-merge-structure-and-expand-comments.patch
mm-further-refactor-commit_merge.patch
mm-eliminate-adj_start-parameter-from-commit_merge.patch
mm-make-vmg-target-consistent-and-further-simplify-commit_merge.patch
mm-completely-abstract-unnecessary-adj_start-calculation.patch
mm-refactor-rmap_walk_file-to-separate-out-traversal-logic.patch
mm-provide-mapping_wrprotect_page-function.patch
fb_defio-do-not-use-deprecated-page-mapping-index-fields.patch
