From: Kevin Brodsky <kevin.brodsky@arm.com>
Date: Mon, 15 Dec 2025 15:03:17 +0000 (+0000)
Subject: mm: bail out of lazy_mmu_mode_* in interrupt context
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9273dfaeaca8ea4d88c7e9fd081922a029984fd4;p=thirdparty%2Flinux.git

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 b81c688426a9 ("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>
---

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index f7d66c2613476..bf9178902bdb4 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -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);
 }
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 116a18b7916c4..dddde6873d1ed 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -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