[PATCH v1 0/4] mm: Fix apply_to_pte_range() vs lazy MMU mode

Alexander Gordeev
2025-04-07T15:12:13Z

Hi All,

This series is an attempt to fix the violation of lazy MMU mode context
requirement as described for arch_enter_lazy_mmu_mode():

This mode can only be entered and left under the protection of
the page table locks for all page tables which may be modified.

On s390 if I make arch_enter_lazy_mmu_mode() -> preempt_enable() and
arch_leave_lazy_mmu_mode() -> preempt_disable() I am getting this:

[ 553.332108] preempt_count: 1, expected: 0
[ 553.332117] no locks held by multipathd/2116.
[ 553.332128] CPU: 24 PID: 2116 Comm: multipathd Kdump: loaded Tainted:
[ 553.332139] Hardware name: IBM 3931 A01 701 (LPAR)
[ 553.332146] Call Trace:
[ 553.332152] [<00000000158de23a>] dump_stack_lvl+0xfa/0x150
[ 553.332167] [<0000000013e10d12>] __might_resched+0x57a/0x5e8
[ 553.332178] [<00000000144eb6c2>] __alloc_pages+0x2ba/0x7c0
[ 553.332189] [<00000000144d5cdc>] __get_free_pages+0x2c/0x88
[ 553.332198] [<00000000145663f6>] kasan_populate_vmalloc_pte+0x4e/0x110
[ 553.332207] [<000000001447625c>] apply_to_pte_range+0x164/0x3c8
[ 553.332218] [<000000001448125a>] apply_to_pmd_range+0xda/0x318
[ 553.332226] [<000000001448181c>] __apply_to_page_range+0x384/0x768
[ 553.332233] [<0000000014481c28>] apply_to_page_range+0x28/0x38
[ 553.332241] [<00000000145665da>] kasan_populate_vmalloc+0x82/0x98
[ 553.332249] [<00000000144c88d0>] alloc_vmap_area+0x590/0x1c90
[ 553.332257] [<00000000144ca108>] __get_vm_area_node.constprop.0+0x138/0x260
[ 553.332265] [<00000000144d17fc>] __vmalloc_node_range+0x134/0x360
[ 553.332274] [<0000000013d5dbf2>] alloc_thread_stack_node+0x112/0x378
[ 553.332284] [<0000000013d62726>] dup_task_struct+0x66/0x430
[ 553.332293] [<0000000013d63962>] copy_process+0x432/0x4b80
[ 553.332302] [<0000000013d68300>] kernel_clone+0xf0/0x7d0
[ 553.332311] [<0000000013d68bd6>] __do_sys_clone+0xae/0xc8
[ 553.332400] [<0000000013d68dee>] __s390x_sys_clone+0xd6/0x118
[ 553.332410] [<0000000013c9d34c>] do_syscall+0x22c/0x328
[ 553.332419] [<00000000158e7366>] __do_syscall+0xce/0xf0
[ 553.332428] [<0000000015913260>] system_call+0x70/0x98

This exposes a KASAN issue fixed with patch 1 and apply_to_pte_range()
issue fixed with patches 2-3. Patch 4 is a debug improvement on top,
that could have helped to notice the issue.

Commit b9ef323ea168 ("powerpc/64s: Disable preemption in hash lazy mmu
mode") looks like powerpc-only fix, yet not entirely conforming to the
above provided requirement (page tables itself are still not protected).
If I am not mistaken, xen and sparc are alike.

Thanks!

Alexander Gordeev (4):
kasan: Avoid sleepable page allocation from atomic context
mm: Cleanup apply_to_pte_range() routine
mm: Protect kernel pgtables in apply_to_pte_range()
mm: Allow detection of wrong arch_enter_lazy_mmu_mode() context

include/linux/pgtable.h | 15 ++++++++++++---
mm/kasan/shadow.c | 9 +++------
mm/memory.c | 33 +++++++++++++++++++++------------
3 files changed, 36 insertions(+), 21 deletions(-)

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2.45.2