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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Jun 2025 04:11:06.9577 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ad0ed990-8e79-47ff-5904-08ddaee750a9 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: AM4PEPF00027A6C.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DU0PR08MB8834 On 15/06/25 1:02 pm, Mike Rapoport wrote: > On Fri, Jun 13, 2025 at 07:13:51PM +0530, Dev Jain wrote: >> -/* >> - * This function assumes that the range is mapped with PAGE_SIZE pages. >> - */ >> -static int __change_memory_common(unsigned long start, unsigned long size, >> +static int ___change_memory_common(unsigned long start, unsigned long size, >> pgprot_t set_mask, pgprot_t clear_mask) >> { >> struct page_change_data data; >> @@ -61,9 +140,28 @@ static int __change_memory_common(unsigned long start, unsigned long size, >> data.set_mask = set_mask; >> data.clear_mask = clear_mask; >> >> - ret = apply_to_page_range(&init_mm, start, size, change_page_range, >> - &data); >> + arch_enter_lazy_mmu_mode(); >> + >> + /* >> + * The caller must ensure that the range we are operating on does not >> + * partially overlap a block mapping. Any such case should either not >> + * exist, or must be eliminated by splitting the mapping - which for >> + * kernel mappings can be done only on BBML2 systems. >> + * >> + */ >> + ret = walk_kernel_page_table_range_lockless(start, start + size, >> + &pageattr_ops, NULL, &data); > x86 has a cpa_lock for set_memory/set_direct_map to ensure that there's on > concurrency in kernel page table updates. I think arm64 has to have such > lock as well. My understanding is that it is guaranteed that the set_memory_* caller has exclusive access to the range it is changing permissions for. The x86 comment is Serialize cpa() (for !DEBUG_PAGEALLOC which uses large identity mappings) using cpa_lock. So that we don't allow any other cpu, with stale large tlb entries change the page attribute in parallel to some other cpu splitting a large page entry along with changing the attribute. On arm64 we are doing flush_tlb_kernel_range in __change_memory_common; and also, the caller of __change_memory_common is required to first split the start and end before changing permissions, so the splitting and permission change won't happen in parallel as described by the comment. > >> + arch_leave_lazy_mmu_mode(); >> + >> + return ret; >> +}