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From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: Will Deacon <will@kernel.org>,
	kernel-team@android.com, linux-kernel@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>
Subject: [PATCH] arm64: mm: Make flush_tlb_fix_spurious_fault() a no-op
Date: Wed, 30 Sep 2020 14:18:59 +0100	[thread overview]
Message-ID: <20200930131859.16989-1-will@kernel.org> (raw)

Our use of broadcast TLB maintenance means that spurious page-faults
that have been handled already by another CPU do not require additional
TLB maintenance.

Make flush_tlb_fix_spurious_fault() a no-op and rely on the existing TLB
invalidation instead. Add an explicit flush_tlb_page() when making a page
dirty, as the TLB is permitted to cache the old read-only entry.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20200728092220.GA21800@willie-the-truck
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/pgtable.h | 8 ++++++++
 arch/arm64/mm/fault.c            | 4 +++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index bc68da9f5706..02ad3105c14c 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -50,6 +50,14 @@ extern void __pgd_error(const char *file, int line, unsigned long val);
 	__flush_tlb_range(vma, addr, end, PUD_SIZE, false, 1)
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
+/*
+ * Outside of a few very special situations (e.g. hibernation), we always
+ * use broadcast TLB invalidation instructions, therefore a spurious page
+ * fault on one CPU which has been handled concurrently by another CPU
+ * does not need to perform additional invalidation.
+ */
+#define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)
+
 /*
  * ZERO_PAGE is a global shared page that is always zero: used
  * for zero-mapped memory areas etc..
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index f07333e86c2f..a696a7921da4 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -218,7 +218,9 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
 		pteval = cmpxchg_relaxed(&pte_val(*ptep), old_pteval, pteval);
 	} while (pteval != old_pteval);
 
-	flush_tlb_fix_spurious_fault(vma, address);
+	/* Invalidate a stale read-only entry */
+	if (dirty)
+		flush_tlb_page(vma, address);
 	return 1;
 }
 
-- 
2.28.0.709.gb0816b6eb0-goog


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WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org, kernel-team@android.com,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>
Subject: [PATCH] arm64: mm: Make flush_tlb_fix_spurious_fault() a no-op
Date: Wed, 30 Sep 2020 14:18:59 +0100	[thread overview]
Message-ID: <20200930131859.16989-1-will@kernel.org> (raw)

Our use of broadcast TLB maintenance means that spurious page-faults
that have been handled already by another CPU do not require additional
TLB maintenance.

Make flush_tlb_fix_spurious_fault() a no-op and rely on the existing TLB
invalidation instead. Add an explicit flush_tlb_page() when making a page
dirty, as the TLB is permitted to cache the old read-only entry.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20200728092220.GA21800@willie-the-truck
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/include/asm/pgtable.h | 8 ++++++++
 arch/arm64/mm/fault.c            | 4 +++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index bc68da9f5706..02ad3105c14c 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -50,6 +50,14 @@ extern void __pgd_error(const char *file, int line, unsigned long val);
 	__flush_tlb_range(vma, addr, end, PUD_SIZE, false, 1)
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
+/*
+ * Outside of a few very special situations (e.g. hibernation), we always
+ * use broadcast TLB invalidation instructions, therefore a spurious page
+ * fault on one CPU which has been handled concurrently by another CPU
+ * does not need to perform additional invalidation.
+ */
+#define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)
+
 /*
  * ZERO_PAGE is a global shared page that is always zero: used
  * for zero-mapped memory areas etc..
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index f07333e86c2f..a696a7921da4 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -218,7 +218,9 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
 		pteval = cmpxchg_relaxed(&pte_val(*ptep), old_pteval, pteval);
 	} while (pteval != old_pteval);
 
-	flush_tlb_fix_spurious_fault(vma, address);
+	/* Invalidate a stale read-only entry */
+	if (dirty)
+		flush_tlb_page(vma, address);
 	return 1;
 }
 
-- 
2.28.0.709.gb0816b6eb0-goog


             reply	other threads:[~2020-09-30 13:20 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-30 13:18 Will Deacon [this message]
2020-09-30 13:18 ` [PATCH] arm64: mm: Make flush_tlb_fix_spurious_fault() a no-op Will Deacon
2020-09-30 17:14 ` Catalin Marinas
2020-09-30 17:14   ` Catalin Marinas

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