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 zzP1xvqE hbveUNf9YZyG+qAda7tQ5gQpRjG1kUrs5+n/lghodt5tDHe/T58XpSJ/LB/xPigHJsa9AeOHc/p9+/Ng1JoI66JUBgtsKbsD+lWVzjfXRcUV324c0JYSB8oteZU0706LFx54xIVO9mkWFnPpmsS8zS39ZXx06fh0fIg04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Aug 12, 2025 at 05:59:02PM +0900, Harry Yoo wrote: > 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(). That's great thanks! > > > > 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. > */ > That's great also, thanks! > -- > 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 > > > >