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charset="utf-8" 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_range() - which allows for this operation to be performed for a specified address_space, offset, PFN and size, without requiring a folio nor, of course, an inappropriate use of page->index, mapping. With this provided, we can subsequently 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 and mapping fields. Signed-off-by: Lorenzo Stoakes --- include/linux/rmap.h | 3 ++ mm/rmap.c | 74 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 77 insertions(+) diff --git a/include/linux/rmap.h b/include/linux/rmap.h index 4509a43fe59f..e28622ee4648 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -754,6 +754,9 @@ unsigned long page_address_in_vma(const struct folio *f= olio, */ int folio_mkclean(struct folio *); =20 +int mapping_wrprotect_range(struct address_space *mapping, pgoff_t pgoff, + unsigned long pfn, unsigned long nr_pages); + int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t p= goff, struct vm_area_struct *vma); =20 diff --git a/mm/rmap.c b/mm/rmap.c index 52f98f6ccb56..66cc318925bc 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1129,6 +1129,80 @@ int folio_mkclean(struct folio *folio) } EXPORT_SYMBOL_GPL(folio_mkclean); =20 +struct wrprotect_file_state { + int cleaned; + pgoff_t pgoff; + unsigned long pfn; + unsigned long nr_pages; +}; + +static bool mapping_wrprotect_range_one(struct folio *folio, + struct vm_area_struct *vma, unsigned long address, void *arg) +{ + struct wrprotect_file_state *state =3D (struct wrprotect_file_state *)arg; + struct page_vma_mapped_walk pvmw =3D { + .pfn =3D state->pfn, + .nr_pages =3D state->nr_pages, + .pgoff =3D state->pgoff, + .vma =3D vma, + .address =3D address, + .flags =3D PVMW_SYNC, + }; + + state->cleaned +=3D page_vma_mkclean_one(&pvmw); + + return true; +} + +static void __rmap_walk_file(struct folio *folio, struct address_space *ma= pping, + pgoff_t pgoff_start, unsigned long nr_pages, + struct rmap_walk_control *rwc, bool locked); + +/** + * mapping_wrprotect_range() - Write-protect all mappings in a specified r= ange. + * + * @mapping: The mapping whose reverse mapping should be traversed. + * @pgoff: The page offset at which @pfn is mapped within @mapping. + * @pfn: The PFN of the page mapped in @mapping at @pgoff. + * @nr_pages: The number of physically contiguous base pages spanned. + * + * Traverses the reverse mapping, finding all VMAs which contain a shared + * mapping of the pages in the specified range in @mapping, and write-prot= ects + * them (that is, updates the page tables to mark the mappings read-only s= uch + * that a write protection fault arises when the mappings are written to). + * + * The @pfn value need not refer to a folio, but rather can reference a ke= rnel + * allocation which is mapped into userland. We therefore do not require t= hat + * the page maps to a folio with a valid mapping or index field, rather the + * caller specifies these in @mapping and @pgoff. + * + * Return: the number of write-protected PTEs, or an error. + */ +int mapping_wrprotect_range(struct address_space *mapping, pgoff_t pgoff, + unsigned long pfn, unsigned long nr_pages) +{ + struct wrprotect_file_state state =3D { + .cleaned =3D 0, + .pgoff =3D pgoff, + .pfn =3D pfn, + .nr_pages =3D nr_pages, + }; + struct rmap_walk_control rwc =3D { + .arg =3D (void *)&state, + .rmap_one =3D mapping_wrprotect_range_one, + .invalid_vma =3D invalid_mkclean_vma, + }; + + if (!mapping) + return 0; + + __rmap_walk_file(/* folio =3D */NULL, mapping, pgoff, nr_pages, &rwc, + /* locked =3D */false); + + return state.cleaned; +} +EXPORT_SYMBOL_GPL(mapping_wrprotect_range); + /** * pfn_mkclean_range - Cleans the PTEs (including PMDs) mapped with range = of * [@pfn, @pfn + @nr_pages) at the specific offset (@p= goff) --=20 2.48.1