[PATCH 1/3] Change enter_lazy_tlb to inline on x86

Xie Yuanbin
2025-10-24T18:27:46Z

This function is very short, and is called in the context switching,
so it is called very frequently.

Change it to inline function on x86 to improve performance, just like
its code in other architectures

Signed-off-by: Xie Yuanbin <qq570070308@gmail.com>
---
arch/x86/include/asm/mmu_context.h | 22 +++++++++++++++++++++-
arch/x86/mm/tlb.c | 21 ---------------------
2 files changed, 21 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 73bf3b1b44e8..30e68c5ef798 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -129,22 +129,42 @@ static inline unsigned long mm_lam_cr3_mask(struct mm_struct *mm)

static inline void dup_lam(struct mm_struct *oldmm, struct mm_struct *mm)
{
}

static inline void mm_reset_untag_mask(struct mm_struct *mm)
{
}
#endif

+/*
+ * Please ignore the name of this function. It should be called
+ * switch_to_kernel_thread().
+ *
+ * enter_lazy_tlb() is a hint from the scheduler that we are entering a
+ * kernel thread or other context without an mm. Acceptable implementations
+ * include doing nothing whatsoever, switching to init_mm, or various clever
+ * lazy tricks to try to minimize TLB flushes.
+ *
+ * The scheduler reserves the right to call enter_lazy_tlb() several times
+ * in a row. It will notify us that we're going back to a real mm by
+ * calling switch_mm_irqs_off().
+ */
#define enter_lazy_tlb enter_lazy_tlb
-extern void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk);
+static __always_inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
+{
+ if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm)
+ return;
+
+ this_cpu_write(cpu_tlbstate_shared.is_lazy, true);
+}
+

#define mm_init_global_asid mm_init_global_asid
extern void mm_init_global_asid(struct mm_struct *mm);

extern void mm_free_global_asid(struct mm_struct *mm);

/*
* Init a new mm. Used on mm copies, like at fork()
* and on mm's that are brand-new, like at execve().
*/
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 5d221709353e..cb715e8e75e4 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -963,41 +963,20 @@ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next,
this_cpu_write(cpu_tlbstate.loaded_mm, next);
this_cpu_write(cpu_tlbstate.loaded_mm_asid, ns.asid);
cpu_tlbstate_update_lam(new_lam, mm_untag_mask(next));

if (next != prev) {
cr4_update_pce_mm(next);
switch_ldt(prev, next);
}
}

-/*
- * Please ignore the name of this function. It should be called
- * switch_to_kernel_thread().
- *
- * enter_lazy_tlb() is a hint from the scheduler that we are entering a
- * kernel thread or other context without an mm. Acceptable implementations
- * include doing nothing whatsoever, switching to init_mm, or various clever
- * lazy tricks to try to minimize TLB flushes.
- *
- * The scheduler reserves the right to call enter_lazy_tlb() several times
- * in a row. It will notify us that we're going back to a real mm by
- * calling switch_mm_irqs_off().
- */
-void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
-{
- if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm)
- return;
-
- this_cpu_write(cpu_tlbstate_shared.is_lazy, true);
-}
-
/*
* Using a temporary mm allows to set temporary mappings that are not accessible
* by other CPUs. Such mappings are needed to perform sensitive memory writes
* that override the kernel memory protections (e.g., W^X), without exposing the
* temporary page-table mappings that are required for these write operations to
* other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the
* mapping is torn down. Temporary mms can also be used for EFI runtime service
* calls or similar functionality.
*
* It is illegal to schedule while using a temporary mm -- the context switch
--
2.51.0