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1VcOGhAnfGnQf6ssh51Wixw6xaF8drORNWSJGMOA+98/+iQIgPpD0mT+NRU4piVj9JhSczO3xAg M9Y6JK5GxlrUMIDzK9ouA76HnQ5NV9//f0hxx29jhzNQ3BwoMK606Nxz+KQrdLu9x+jMTbzt8Zt NneAS0wMlKYlKZP0USvWGeAl8ML2y6pUGjDPUhckVSrvY+MkiN4NMm70CdU65XIPfQnEJ9r/Acv ApOhkYxN08ptzoTSp0smwSIWtHXVhwdbwRXc48ffGe/2wNx0DQdsSjz1jflnIl+HnfopzmHy X-Authority-Analysis: v=2.4 cv=eIsTjGp1 c=1 sm=1 tr=0 ts=689b0271 b=1 cx=c_pps a=qoll8+KPOyaMroiJ2sR5sw==:117 a=qoll8+KPOyaMroiJ2sR5sw==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=2OwXVqhp2XgA:10 a=GoEa3M9JfhUA:10 a=VwQbUJbxAAAA:8 a=QyXUC8HyAAAA:8 a=yPCof4ZbAAAA:8 a=Em3zR9OIEgInuRs0RJ8A:9 a=CjuIK1q_8ugA:10 cc=ntf awl=host:12070 X-Proofpoint-GUID: rYTTiGDbbxOlp_vk2wgYCFQAf6Y49Ckh X-Proofpoint-ORIG-GUID: rYTTiGDbbxOlp_vk2wgYCFQAf6Y49Ckh On Mon, Aug 11, 2025 at 12:46:32PM +0100, Lorenzo Stoakes wrote: > On Mon, Aug 11, 2025 at 02:34:20PM +0900, Harry Yoo wrote: > > Define ARCH_PAGE_TABLE_SYNC_MASK and arch_sync_kernel_mappings() to ensure > > page tables are properly synchronized when calling p*d_populate_kernel(). > > It is inteneded to synchronize page tables via pgd_pouplate_kernel() when > > 5-level paging is in use and via p4d_pouplate_kernel() when 4-level paging > > is used. > > > > I think it's worth mentioning here that pgd_populate() is a no-op in 4-level > systems, so the sychronisation must occur at the P4D level, just to make this > clear. Yeah, that's indeed confusing and agree that it's worth mentioning. Will do. The new one: Define ARCH_PAGE_TABLE_SYNC_MASK and arch_sync_kernel_mappings() to ensure page tables are properly synchronized when calling p*d_populate_kernel(). For 5-level paging, synchronization is performed via pgd_populate_kernel(). In 4-level paging, pgd_populate() is a no-op, so synchronization is instead performed at the P4D level via p4d_populate_kernel(). > > This fixes intermittent boot failures on systems using 4-level paging > > and a large amount of persistent memory: > > > > BUG: unable to handle page fault for address: ffffe70000000034 > > #PF: supervisor write access in kernel mode > > #PF: error_code(0x0002) - not-present page > > PGD 0 P4D 0 > > Oops: 0002 [#1] SMP NOPTI > > RIP: 0010:__init_single_page+0x9/0x6d > > Call Trace: > > > > __init_zone_device_page+0x17/0x5d > > memmap_init_zone_device+0x154/0x1bb > > pagemap_range+0x2e0/0x40f > > memremap_pages+0x10b/0x2f0 > > devm_memremap_pages+0x1e/0x60 > > dev_dax_probe+0xce/0x2ec [device_dax] > > dax_bus_probe+0x6d/0xc9 > > [... snip ...] > > > > > > It also fixes a crash in vmemmap_set_pmd() caused by accessing vmemmap > > before sync_global_pgds() [1]: > > > > BUG: unable to handle page fault for address: ffffeb3ff1200000 > > #PF: supervisor write access in kernel mode > > #PF: error_code(0x0002) - not-present page > > PGD 0 P4D 0 > > Oops: Oops: 0002 [#1] PREEMPT SMP NOPTI > > Tainted: [W]=WARN > > RIP: 0010:vmemmap_set_pmd+0xff/0x230 > > > > vmemmap_populate_hugepages+0x176/0x180 > > vmemmap_populate+0x34/0x80 > > __populate_section_memmap+0x41/0x90 > > sparse_add_section+0x121/0x3e0 > > __add_pages+0xba/0x150 > > add_pages+0x1d/0x70 > > memremap_pages+0x3dc/0x810 > > devm_memremap_pages+0x1c/0x60 > > xe_devm_add+0x8b/0x100 [xe] > > xe_tile_init_noalloc+0x6a/0x70 [xe] > > xe_device_probe+0x48c/0x740 [xe] > > [... snip ...] > > > > Cc: > > Fixes: 8d400913c231 ("x86/vmemmap: handle unpopulated sub-pmd ranges") > > Closes: https://lore.kernel.org/linux-mm/20250311114420.240341-1-gwan-gyeong.mun@intel.com [1] > > Suggested-by: Dave Hansen > > Signed-off-by: Harry Yoo > > Other than nitty comments, this looks good to me, so: > > Reviewed-by: Lorenzo Stoakes Thanks! > > --- > > arch/x86/include/asm/pgtable_64_types.h | 3 +++ > > arch/x86/mm/init_64.c | 5 +++++ > > 2 files changed, 8 insertions(+) > > > > diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h > > index 4604f924d8b8..7eb61ef6a185 100644 > > --- a/arch/x86/include/asm/pgtable_64_types.h > > +++ b/arch/x86/include/asm/pgtable_64_types.h > > @@ -36,6 +36,9 @@ static inline bool pgtable_l5_enabled(void) > > #define pgtable_l5_enabled() cpu_feature_enabled(X86_FEATURE_LA57) > > #endif /* USE_EARLY_PGTABLE_L5 */ > > > > +#define ARCH_PAGE_TABLE_SYNC_MASK \ > > + (pgtable_l5_enabled() ? PGTBL_PGD_MODIFIED : PGTBL_P4D_MODIFIED) > > + > > extern unsigned int pgdir_shift; > > extern unsigned int ptrs_per_p4d; > > > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > > index 76e33bd7c556..a78b498c0dc3 100644 > > --- a/arch/x86/mm/init_64.c > > +++ b/arch/x86/mm/init_64.c > > @@ -223,6 +223,11 @@ static void sync_global_pgds(unsigned long start, unsigned long end) > > sync_global_pgds_l4(start, end); > > } > > > > Worth a comment to say 'if 4-level, then we synchronise at P4D level by > convention, however the same sync_global_pgds() applies'? Maybe: /* * Make kernel mappings visible in all page tables in the system. * This is necessary except when the init task populates kernel mappings * during the boot process. In that case, all processes originating from * the init task copies the kernel mappings, so there is no issue. * Otherwise, missing synchronization could lead to kernel crashes due * to missing page table entries for certain kernel mappings. * * Synchronization is performed at the top level, which is the PGD in * 5-level paging systems. But in 4-level paging systems, however, * pgd_populate() is a no-op, so synchronization is done at P4D level instead. * sync_global_pgds() handles this difference between paging levels. */ -- Cheers, Harry / Hyeonggon > > +void arch_sync_kernel_mappings(unsigned long start, unsigned long end) > > +{ > > + sync_global_pgds(start, end); > > +} > > + > > /* > > * NOTE: This function is marked __ref because it calls __init function > > * (alloc_bootmem_pages). It's safe to do it ONLY when after_bootmem == 0. > > -- > > 2.43.0 > >