linux-kernel - [PATCH v4 12/12] riscv: mm: Always use an ASID to flush mm contexts

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Date: Tue,  2 Jan 2024 14:00:49 -0800
From: Samuel Holland <samuel.holland@...ive.com>
To: Palmer Dabbelt <palmer@...belt.com>,
	linux-riscv@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	Samuel Holland <samuel.holland@...ive.com>
Subject: [PATCH v4 12/12] riscv: mm: Always use an ASID to flush mm contexts

Even if multiple ASIDs are not supported, using the single-ASID variant
of the sfence.vma instruction preserves TLB entries for global (kernel)
pages. So it is always more efficient to use the single-ASID code path.

Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---

Changes in v4:
 - There is now only one copy of __flush_tlb_range()

Changes in v2:
 - Update both copies of __flush_tlb_range()

 arch/riscv/include/asm/mmu_context.h | 2 --
 arch/riscv/mm/context.c              | 3 +--
 arch/riscv/mm/tlbflush.c             | 3 +--
 3 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h
index 7030837adc1a..b0659413a080 100644
--- a/arch/riscv/include/asm/mmu_context.h
+++ b/arch/riscv/include/asm/mmu_context.h
@@ -33,8 +33,6 @@ static inline int init_new_context(struct task_struct *tsk,
 	return 0;
 }
 
-DECLARE_STATIC_KEY_FALSE(use_asid_allocator);
-
 #include <asm-generic/mmu_context.h>
 
 #endif /* _ASM_RISCV_MMU_CONTEXT_H */
diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
index 3ca9b653df7d..20057085ab8a 100644
--- a/arch/riscv/mm/context.c
+++ b/arch/riscv/mm/context.c
@@ -18,8 +18,7 @@
 
 #ifdef CONFIG_MMU
 
-DEFINE_STATIC_KEY_FALSE(use_asid_allocator);
-
+static DEFINE_STATIC_KEY_FALSE(use_asid_allocator);
 static unsigned long num_asids;
 
 static atomic_long_t current_version;
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 5ec621545c69..39d80f56d292 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -84,8 +84,7 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
 		if (cpumask_empty(cmask))
 			return;
 
-		if (static_branch_unlikely(&use_asid_allocator))
-			asid = cntx2asid(atomic_long_read(&mm->context.id));
+		asid = cntx2asid(atomic_long_read(&mm->context.id));
 	} else {
 		cmask = cpu_online_mask;
 	}
-- 
2.42.0