linux-kernel - [PATCH 1/2] mm/tlb: fix fullmm semantics

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Message-Id: <20231228084642.1765-2-jszhang@kernel.org>
Date: Thu, 28 Dec 2023 16:46:41 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: Will Deacon <will@...nel.org>,
	"Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Arnd Bergmann <arnd@...db.de>
Cc: linux-arch@...r.kernel.org,
	linux-mm@...ck.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	Nadav Amit <namit@...are.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yu Zhao <yuzhao@...gle.com>,
	x86@...nel.org
Subject: [PATCH 1/2] mm/tlb: fix fullmm semantics

From: Nadav Amit <namit@...are.com>

fullmm in mmu_gather is supposed to indicate that the mm is torn-down
(e.g., on process exit) and can therefore allow certain optimizations.
However, tlb_finish_mmu() sets fullmm, when in fact it want to say that
the TLB should be fully flushed.

Change tlb_finish_mmu() to set need_flush_all and check this flag in
tlb_flush_mmu_tlbonly() when deciding whether a flush is needed.

At the same time, bring the arm64 fullmm on process exit optimization back.

Signed-off-by: Nadav Amit <namit@...are.com>
Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Deacon <will@...nel.org>
Cc: Yu Zhao <yuzhao@...gle.com>
Cc: Nick Piggin <npiggin@...il.com>
Cc: x86@...nel.org
---
 arch/arm64/include/asm/tlb.h | 5 ++++-
 include/asm-generic/tlb.h    | 2 +-
 mm/mmu_gather.c              | 2 +-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
index 846c563689a8..6164c5f3b78f 100644
--- a/arch/arm64/include/asm/tlb.h
+++ b/arch/arm64/include/asm/tlb.h
@@ -62,7 +62,10 @@ static inline void tlb_flush(struct mmu_gather *tlb)
 	 * invalidating the walk-cache, since the ASID allocator won't
 	 * reallocate our ASID without invalidating the entire TLB.
 	 */
-	if (tlb->fullmm) {
+	if (tlb->fullmm)
+		return;
+
+	if (tlb->need_flush_all) {
 		if (!last_level)
 			flush_tlb_mm(tlb->mm);
 		return;
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 129a3a759976..f2d46357bcbb 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -452,7 +452,7 @@ static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
 	 * these bits.
 	 */
 	if (!(tlb->freed_tables || tlb->cleared_ptes || tlb->cleared_pmds ||
-	      tlb->cleared_puds || tlb->cleared_p4ds))
+	      tlb->cleared_puds || tlb->cleared_p4ds || tlb->need_flush_all))
 		return;
 
 	tlb_flush(tlb);
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index 4f559f4ddd21..79298bac3481 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -384,7 +384,7 @@ void tlb_finish_mmu(struct mmu_gather *tlb)
 		 * On x86 non-fullmm doesn't yield significant difference
 		 * against fullmm.
 		 */
-		tlb->fullmm = 1;
+		tlb->need_flush_all = 1;
 		__tlb_reset_range(tlb);
 		tlb->freed_tables = 1;
 	}
-- 
2.40.0