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Sat, 8 Feb 2025 15:53:14 +0000 Received: from BYAPR10MB3366.namprd10.prod.outlook.com ([fe80::baf2:dff1:d471:1c9]) by BYAPR10MB3366.namprd10.prod.outlook.com ([fe80::baf2:dff1:d471:1c9%4]) with mapi id 15.20.8398.025; Sat, 8 Feb 2025 15:53:14 +0000 From: Lorenzo Stoakes To: Andrew Morton Cc: Jaya Kumar , Simona Vetter , Helge Deller , linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox , David Hildenbrand , Kajtar Zsolt , Maira Canal , Simona Vetter , Thomas Zimmermann Subject: [PATCH v3 2/3] mm: provide mapping_wrprotect_range() function Date: Sat, 8 Feb 2025 15:52:55 +0000 Message-ID: X-Mailer: git-send-email 2.48.1 In-Reply-To: References: X-ClientProxiedBy: LO2P123CA0037.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600::25) To BYAPR10MB3366.namprd10.prod.outlook.com (2603:10b6:a03:14f::25) Precedence: bulk X-Mailing-List: linux-fbdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR10MB3366:EE_|PH0PR10MB5817:EE_ X-MS-Office365-Filtering-Correlation-Id: 354f6022-4b73-42be-e447-08dd4858b27c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|1800799024; 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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 *folio, */ int folio_mkclean(struct folio *); +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 pgoff, struct vm_area_struct *vma); 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); +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 = (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_range() - Write-protect all mappings in a specified range. + * + * @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-protects + * them (that is, updates the page tables to mark the mappings read-only such + * 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 kernel + * allocation which is mapped into userland. We therefore do not require that + * 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 = { + .cleaned = 0, + .pgoff = pgoff, + .pfn = pfn, + .nr_pages = nr_pages, + }; + struct rmap_walk_control rwc = { + .arg = (void *)&state, + .rmap_one = mapping_wrprotect_range_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_range); + /** * pfn_mkclean_range - Cleans the PTEs (including PMDs) mapped with range of * [@pfn, @pfn + @nr_pages) at the specific offset (@pgoff)