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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Jan 2026 21:25:57.2787 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f082b398-8b17-4a61-3779-08de57a155ca 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: AM4PEPF00027A66.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV2PR08MB8123 Hi Will, > On Mon, Jan 05, 2026 at 08:23:27PM +0000, Yeoreum Yun wrote: > > +static int __init linear_map_prealloc_split_pgtables(void) > > +{ > > + int ret, i; > > + unsigned long lstart = _PAGE_OFFSET(vabits_actual); > > + unsigned long lend = PAGE_END; > > + unsigned long kstart = (unsigned long)lm_alias(_stext); > > + unsigned long kend = (unsigned long)lm_alias(__init_begin); > > + > > + const struct mm_walk_ops collect_to_split_ops = { > > + .pud_entry = collect_to_split_pud_entry, > > + .pmd_entry = collect_to_split_pmd_entry > > + }; > > Why do we need to rewalk the page-table here instead of collating the > number of block mappings we put down when creating the linear map in > the first place? First, linear alias of the [_text, __init_begin) is not a target for the split and it also seems strange to me to add code inside alloc_init_XXX() that both checks an address range and counts to get the number of block mappings. Second, for a future feature, I hope to add some code to split "specfic" area to be spilt e.x) to set a specific pkey for specific area. In this case, it's useful to rewalk the page-table with the specific range to get the number of block mapping. > > > + split_pgtables_idx = 0; > > + split_pgtables_count = 0; > > + > > + ret = walk_kernel_page_table_range_lockless(lstart, kstart, > > + &collect_to_split_ops, > > + NULL, NULL); > > + if (!ret) > > + ret = walk_kernel_page_table_range_lockless(kend, lend, > > + &collect_to_split_ops, > > + NULL, NULL); > > + if (ret || !split_pgtables_count) > > + goto error; > > + > > + ret = -ENOMEM; > > + > > + split_pgtables = kvmalloc(split_pgtables_count * sizeof(struct ptdesc *), > > + GFP_KERNEL | __GFP_ZERO); > > + if (!split_pgtables) > > + goto error; > > + > > + for (i = 0; i < split_pgtables_count; i++) { > > + /* The page table will be filled during splitting, so zeroing it is unnecessary. */ > > + split_pgtables[i] = pagetable_alloc(GFP_PGTABLE_KERNEL & ~__GFP_ZERO, 0); > > + if (!split_pgtables[i]) > > + goto error; > > This looks potentially expensive on the boot path and only gets worse as > the amount of memory grows. Maybe we should predicate this preallocation > on preempt-rt? Agree. then I'll apply pre-allocation with PREEMPT_RT only. Thanks for your review. -- Sincerely, Yeoreum Yun