CVE-2025-39845

In the Linux kernel, the following vulnerability has been resolved:

x86/mm/64: define ARCHPAGETABLESYNCMASK and archsynckernel_mappings()

Define ARCHPAGETABLESYNCMASK and archsynckernelmappings() to ensure page tables are properly synchronized when calling p*dpopulate_kernel().

For 5-level paging, synchronization is performed via pgdpopulatekernel(). In 4-level paging, pgdpopulate() is a no-op, so synchronization is instead performed at the P4D level via p4dpopulate_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: errorcode(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI RIP: 0010:initsinglepage+0x9/0x6d Call Trace: <TASK> _initzonedevicepage+0x17/0x5d memmapinitzonedevice+0x154/0x1bb pagemaprange+0x2e0/0x40f memremappages+0x10b/0x2f0 devmmemremappages+0x1e/0x60 devdaxprobe+0xce/0x2ec [devicedax] daxbus_probe+0x6d/0xc9 [... snip ...] </TASK>

It also fixes a crash in vmemmapsetpmd() caused by accessing vmemmap before syncglobalpgds() [1]:

BUG: unable to handle page fault for address: ffffeb3ff1200000 #PF: supervisor write access in kernel mode #PF: errorcode(0x0002) - not-present page PGD 0 P4D 0 Oops: Oops: 0002 [#1] PREEMPT SMP NOPTI Tainted: [W]=WARN RIP: 0010:vmemmapsetpmd+0xff/0x230 <TASK> vmemmappopulatehugepages+0x176/0x180 vmemmappopulate+0x34/0x80 _populatesectionmemmap+0x41/0x90 sparseaddsection+0x121/0x3e0 _addpages+0xba/0x150 addpages+0x1d/0x70 memremappages+0x3dc/0x810 devmmemremappages+0x1c/0x60 xedevmadd+0x8b/0x100 [xe] xetileinitnoalloc+0x6a/0x70 [xe] xedeviceprobe+0x48c/0x740 [xe] [... snip ...]