Commit 9273dfae authored Dec 15, 2025 by Kevin Brodsky Committed by Andrew Morton Jan 20, 2026

mm: bail out of lazy_mmu_mode_* in interrupt context

The lazy MMU mode cannot be used in interrupt context.  This is documented
in <linux/pgtable.h>, but isn't consistently handled across architectures.

arm64 ensures that calls to lazy_mmu_mode_* have no effect in interrupt
context, because such calls do occur in certain configurations - see
commit b81c6884 ("arm64/mm: Disable barrier batching in interrupt
contexts").  Other architectures do not check this situation, most likely
because it hasn't occurred so far.

Let's handle this in the new generic lazy_mmu layer, in the same fashion
as arm64: bail out of lazy_mmu_mode_* if in_interrupt().  Also remove the
arm64 handling that is now redundant.

Both arm64 and x86/Xen also ensure that any lazy MMU optimisation is
disabled while in interrupt (see queue_pte_barriers() and
xen_get_lazy_mode() respectively).  This will be handled in the generic
layer in a subsequent patch.

Link: https://lkml.kernel.org/r/20251215150323.2218608-9-kevin.brodsky@arm.com


Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Hildenbrand <david@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Juegren Gross <jgross@suse.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent 0a096ab7

arch/arm64/include/asm/pgtable.h

+0 −9

Original line number	Diff line number	Diff line
		@@ -94,26 +94,17 @@ static inline void arch_enter_lazy_mmu_mode(void)
		* keeps tracking simple.
		*/

		if (in_interrupt())
		return;

		set_thread_flag(TIF_LAZY_MMU);
		}

		static inline void arch_flush_lazy_mmu_mode(void)
		{
		if (in_interrupt())
		return;

		if (test_and_clear_thread_flag(TIF_LAZY_MMU_PENDING))
		emit_pte_barriers();
		}

		static inline void arch_leave_lazy_mmu_mode(void)
		{
		if (in_interrupt())
		return;

		arch_flush_lazy_mmu_mode();
		clear_thread_flag(TIF_LAZY_MMU);
		}

include/linux/pgtable.h

+16 −1

Original line number	Diff line number	Diff line
		@@ -233,26 +233,41 @@ static inline int pmd_dirty(pmd_t pmd)
		* preemption, as a consequence generic code may not sleep while the lazy MMU
		* mode is active.
		*
		* Nesting is not permitted and the mode cannot be used in interrupt context.
		* The mode is disabled in interrupt context and calls to the lazy_mmu API have
		* no effect.
		*
		* Nesting is not permitted.
		*/
		#ifdef CONFIG_ARCH_HAS_LAZY_MMU_MODE
		static inline void lazy_mmu_mode_enable(void)
		{
		if (in_interrupt())
		return;

		arch_enter_lazy_mmu_mode();
		}

		static inline void lazy_mmu_mode_disable(void)
		{
		if (in_interrupt())
		return;

		arch_leave_lazy_mmu_mode();
		}

		static inline void lazy_mmu_mode_pause(void)
		{
		if (in_interrupt())
		return;

		arch_leave_lazy_mmu_mode();
		}

		static inline void lazy_mmu_mode_resume(void)
		{
		if (in_interrupt())
		return;

		arch_enter_lazy_mmu_mode();
		}
		#else