Re: [PATCH v5 07/12] mm: bail out of lazy_mmu_mode_* in interrupt context
From: Anshuman Khandual <hidden>
Date: 2025-12-04 04:34:17
Also in:
linux-arm-kernel, linux-mm, lkml, sparclinux, xen-devel
On 24/11/25 6:52 PM, Kevin Brodsky wrote:
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.Ensuring a common behaviour across platforms such as this in interrupt context bail out - can now be easily achieved now as there are generic helpers that call the platform ones.
quoted
Both arm64 and x86/Xen also ensure that any lazy MMU optimisation isdisabled 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.
Makes sense.
quoted hunk ↗ jump to hunk
Signed-off-by: Kevin Brodsky <redacted> --- arch/arm64/include/asm/pgtable.h | 9 --------- include/linux/pgtable.h | 17 +++++++++++++++-- 2 files changed, 15 insertions(+), 11 deletions(-)diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 54f8d6bb6f22..e596899f4029 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 c121358dba15..8ff6fdb4b13d 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h@@ -228,27 +228,40 @@ static inline int pmd_dirty(pmd_t pmd) * of the lazy mode. So the implementation must assume preemption may be enabled * and cpu migration is possible; it must take steps to be robust against this. * (In practice, for user PTE updates, the appropriate page table lock(s) are - * held, but for kernel PTE updates, no lock is held). Nesting is not permitted - * and the mode cannot be used in interrupt context. + * held, but for kernel PTE updates, no lock is held). The mode is disabled in + * interrupt context and calls to the lazy_mmu API have no effect. + * Nesting is not permitted.
Right - nesting is still not 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();
}
#elseLGTM Reviewed-by: Anshuman Khandual <redacted>