[PATCH V4 mm-hotfixes 3/3] x86/mm/64: define ARCH_PAGE_TABLE_SYNC_MASK and arch_sync_kernel_mappings()

Harry Yoo
2025-08-11T05:35:29Z

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.

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:
<TASK>
__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 ...]
</TASK>

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
<TASK>
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: <stable@vger.kernel.org>
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 <dave.hansen@linux.intel.com>
Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
---
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);
}

+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