Re: [PATCH V5 mm-hotfixes 3/3] x86/mm/64: define ARCH_PAGE_TABLE_SYNC_MASK and arch_sync_kernel_mappings()

[David Hildenbrand]

On 18.08.25 04:02, 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().
>
> 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:
>     <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@xxxxxxxxxxxxxxx>
> Fixes: 8d400913c231 ("x86/vmemmap: handle unpopulated sub-pmd ranges")
> Closes: https://lore.kernel.org/linux-mm/20250311114420.240341-1-gwan-gyeong.mun@xxxxxxxxx [1]
> Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Acked-by: Kiryl Shutsemau <kas@xxxxxxxxxx>
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> Signed-off-by: Harry Yoo <harry.yoo@xxxxxxxxxx>
> ---

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers

David / dhildenb