linux-kernel - [RFC PATCH v2 5/9] riscv: mm: Introduce arch_do_shoot_lazy

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Message-ID: <20251127141117.87420-6-luxu.kernel@bytedance.com>
Date: Thu, 27 Nov 2025 22:11:13 +0800
From: Xu Lu <luxu.kernel@...edance.com>
To: pjw@...nel.org,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	alex@...ti.fr,
	kees@...nel.org,
	mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	vincent.guittot@...aro.org,
	akpm@...ux-foundation.org,
	david@...hat.com,
	apatel@...tanamicro.com,
	guoren@...nel.org
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Xu Lu <luxu.kernel@...edance.com>
Subject: [RFC PATCH v2 5/9] riscv: mm: Introduce arch_do_shoot_lazy_tlb

When an active_mm is shot down, we switch it to the init_mm, evict it
out of percpu active mm array.

Signed-off-by: Xu Lu <luxu.kernel@...edance.com>
---
 arch/riscv/include/asm/mmu_context.h |  5 ++++
 arch/riscv/include/asm/tlbflush.h    | 11 +++++++++
 arch/riscv/mm/context.c              | 19 ++++++++++++++++
 arch/riscv/mm/tlbflush.c             | 34 ++++++++++++++++++++++++----
 4 files changed, 64 insertions(+), 5 deletions(-)

diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h
index 8c4bc49a3a0f5..bc73cc3262ae6 100644
--- a/arch/riscv/include/asm/mmu_context.h
+++ b/arch/riscv/include/asm/mmu_context.h
@@ -16,6 +16,11 @@
 void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 	struct task_struct *task);
 
+#ifdef CONFIG_RISCV_LAZY_TLB_FLUSH
+#define arch_do_shoot_lazy_tlb	arch_do_shoot_lazy_tlb
+void arch_do_shoot_lazy_tlb(void *arg);
+#endif
+
 #define activate_mm activate_mm
 static inline void activate_mm(struct mm_struct *prev,
 			       struct mm_struct *next)
diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index 3f83fd5ef36db..e7365a53265a6 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -15,6 +15,11 @@
 #define FLUSH_TLB_NO_ASID       ((unsigned long)-1)
 
 #ifdef CONFIG_MMU
+static inline unsigned long get_mm_asid(struct mm_struct *mm)
+{
+	return mm ? cntx2asid(atomic_long_read(&mm->context.id)) : FLUSH_TLB_NO_ASID;
+}
+
 static inline void local_flush_tlb_all(void)
 {
 	__asm__ __volatile__ ("sfence.vma" : : : "memory");
@@ -86,11 +91,17 @@ struct tlb_info {
 DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_info, tlbinfo);
 
 void local_load_tlb_mm(struct mm_struct *mm);
+void local_flush_tlb_mm(struct mm_struct *mm);
 
 #else /* CONFIG_RISCV_LAZY_TLB_FLUSH */
 
 static inline void local_load_tlb_mm(struct mm_struct *mm) {}
 
+static inline void local_flush_tlb_mm(struct mm_struct *mm)
+{
+	local_flush_tlb_all_asid(get_mm_asid(mm));
+}
+
 #endif /* CONFIG_RISCV_LAZY_TLB_FLUSH */
 
 #else /* CONFIG_MMU */
diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
index a7cf36ad34678..3335080e5f720 100644
--- a/arch/riscv/mm/context.c
+++ b/arch/riscv/mm/context.c
@@ -274,6 +274,25 @@ static int __init asids_init(void)
 	return 0;
 }
 early_initcall(asids_init);
+
+#ifdef CONFIG_RISCV_LAZY_TLB_FLUSH
+void arch_do_shoot_lazy_tlb(void *arg)
+{
+	struct mm_struct *mm = arg;
+
+	if (current->active_mm == mm) {
+		WARN_ON_ONCE(current->mm);
+		current->active_mm = &init_mm;
+		switch_mm(mm, &init_mm, current);
+	}
+
+	if (!static_branch_unlikely(&use_asid_allocator) || !mm)
+		return;
+
+	local_flush_tlb_mm(mm);
+}
+#endif /* CONFIG_RISCV_LAZY_TLB_FLUSH */
+
 #else
 static inline void set_mm(struct mm_struct *prev,
 			  struct mm_struct *next, unsigned int cpu)
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 4b2ce06cbe6bd..a47bacf5801ab 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -164,11 +164,6 @@ static void __ipi_flush_tlb_range_asid(void *info)
 	local_flush_tlb_range_asid(d->start, d->size, d->stride, d->asid);
 }
 
-static inline unsigned long get_mm_asid(struct mm_struct *mm)
-{
-	return mm ? cntx2asid(atomic_long_read(&mm->context.id)) : FLUSH_TLB_NO_ASID;
-}
-
 static void __flush_tlb_range(struct mm_struct *mm,
 			      const struct cpumask *cmask,
 			      unsigned long start, unsigned long size,
@@ -352,4 +347,33 @@ void local_load_tlb_mm(struct mm_struct *mm)
 	}
 }
 
+void local_flush_tlb_mm(struct mm_struct *mm)
+{
+	struct tlb_info *info = this_cpu_ptr(&tlbinfo);
+	struct tlb_context *contexts = info->contexts;
+	unsigned long asid = get_mm_asid(mm);
+	unsigned int i;
+
+	if (!mm || mm == info->active_mm) {
+		local_flush_tlb_all_asid(asid);
+		return;
+	}
+
+	for (i = 0; i < MAX_LOADED_MM; i++) {
+		if (contexts[i].mm != mm)
+			continue;
+
+		write_lock(&info->rwlock);
+		contexts[i].mm = NULL;
+		contexts[i].gen = 0;
+		write_unlock(&info->rwlock);
+
+		cpumask_clear_cpu(raw_smp_processor_id(), mm_cpumask(mm));
+		mmdrop_lazy_mm(mm);
+		break;
+	}
+
+	local_flush_tlb_all_asid(asid);
+}
+
 #endif /* CONFIG_RISCV_LAZY_TLB_FLUSH */
-- 
2.20.1