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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 May 2025 10:43:00.8140 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 863083f0-1823-4c9a-8081-08dd9f66bfc0 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AMS1EPF00000040.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DU0PR08MB8929 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250530_034306_608257_9E2A067D X-CRM114-Status: GOOD ( 12.01 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 30/05/25 4:07 pm, Ryan Roberts wrote: > On 30/05/2025 11:10, Dev Jain wrote: >> On 30/05/25 3:33 pm, Ryan Roberts wrote: >>> On 30/05/2025 10:04, Dev Jain wrote: >>>> This series paves the path to enable huge mappings in vmalloc space by >>>> default on arm64. > For this we must ensure that we can handle any permission >>>> games on vmalloc space. >>> And the linear map :) >>> >>>> Currently, __change_memory_common() uses >>>> apply_to_page_range() which does not support changing permissions for >>>> leaf mappings. >>> nit: A "leaf mapping" is the lowest level entry in the page tables for a given >>> address - i.e. it maps an address to some actual memory rather than to another >>> pgtable. It includes what the Arm ARM calls "page mappings" (PTE level) and >>> "block mappings" (PMD/PUD/.. level). apply_to_page_range() does support page >>> mappings, so saying it doesn't support leaf mappings is incorrect. It doesn't >>> support block mappings. >> Sorry, again got confused by nomenclature : ) >> >>>> We attempt to move away from this by using walk_page_range_novma(), >>>> similar to what riscv does right now; however, it is the responsibility >>>> of the caller to ensure that we do not pass a range, or split the range >>>> covering a partial leaf mapping. >>>> >>>> This series is tied with Yang Shi's attempt [1] at using huge mappings >>>> in the linear mapping in case the system supports BBML2, in which case >>>> we will be able to split the linear mapping if needed without break-before-make. >>>> Thus, Yang's series, IIUC, will be one such user of my series; suppose we >>>> are changing permissions on a range of the linear map backed by PMD-hugepages, >>>> then the sequence of operations should look like the following: >>>> >>>> split_range(start, (start + HPAGE_PMD_SIZE) & ~HPAGE_PMD_MASK); >>>> split_range(end & ~HPAGE_PMD_MASK, end); >>> I don't understand what the HPAGE_PMD_MASK twiddling is doing? That's not right. >>> It's going to give you the offset within the 2M region. You just want: >>> >>> split_range(start) >>> split_range(end) >>> >>> right? >> Suppose start = 2M + 4K, end = 8M + 5K. Then my sequence will compute to > 8M + 5K is not a valid split point. It has to be at least page aligned. Sorry, so consider 8M + 4K. >> split_range(2M + 4K, 3M) >> split_range(8M, 8M + 5K) > We just want to split at start and end. What are the 3M and 8M params supposed > to be? Anyway, this is off-topic for this series. I think we are both saying the same thing; yes we will split only the start and the end, so if the address 2Mb + 4Kb is mapped as a PMD-hugepage, we need to split this PMD into a PTE table, which will map 2Mb till 4Mb as base pages now. > >> __change_memory_common(2M + 4K, 8M + 5K) >> >> So now __change_memory_common() wouldn't have to deal with splitting the >> starts and ends. Please correct me if I am wrong. >> >>>> __change_memory_common(start, end); >>>> >>>> However, this series can be used independently of Yang's; since currently >>>> permission games are being played only on pte mappings (due to >>>> apply_to_page_range >>>> not supporting otherwise), this series provides the mechanism for enabling >>>> huge mappings for various kernel mappings like linear map and vmalloc. >>> In other words, you are saying that this series is a prerequisite for Yang's >>> series (and both are prerequisites for huge vmalloc by default). Your series >>> adds a new capability that Yang's series will rely on (the ability to change >>> permissions on block mappings). >> That's right. >> >>> Thanks, >>> Ryan >>> >>>> [1] https://lore.kernel.org/all/20250304222018.615808-1- >>>> yang@os.amperecomputing.com/ >>>> >>>> Dev Jain (3): >>>>    mm: Allow pagewalk without locks >>>>    arm64: pageattr: Use walk_page_range_novma() to change memory >>>>      permissions >>>>    mm/pagewalk: Add pre/post_pte_table callback for lazy MMU on arm64 >>>> >>>>   arch/arm64/mm/pageattr.c | 81 +++++++++++++++++++++++++++++++++++++--- >>>>   include/linux/pagewalk.h |  4 ++ >>>>   mm/pagewalk.c            | 18 +++++++-- >>>>   3 files changed, 94 insertions(+), 9 deletions(-) >>>>