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From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	linux-kernel@vger.kernel.org,
	Sami Tolvanen <samitolvanen@google.com>,
	Will Deacon <will@kernel.org>
Subject: [PATCH v4 3/4] arm64: alternatives: Remove READ_ONCE() usage during patch operation
Date: Tue,  3 Nov 2020 12:17:20 +0000	[thread overview]
Message-ID: <20201103121721.5166-4-will@kernel.org> (raw)
In-Reply-To: <20201103121721.5166-1-will@kernel.org>

In preparation for patching the internals of READ_ONCE() itself, replace
its usage on the alternatives patching patch with a volatile variable
instead.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/alternative.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
index 73039949b5ce..a57cffb752e8 100644
--- a/arch/arm64/kernel/alternative.c
+++ b/arch/arm64/kernel/alternative.c
@@ -21,7 +21,8 @@
 #define ALT_ORIG_PTR(a)		__ALT_PTR(a, orig_offset)
 #define ALT_REPL_PTR(a)		__ALT_PTR(a, alt_offset)
 
-static int all_alternatives_applied;
+/* Volatile, as we may be patching the guts of READ_ONCE() */
+static volatile int all_alternatives_applied;
 
 static DECLARE_BITMAP(applied_alternatives, ARM64_NCAPS);
 
@@ -205,7 +206,7 @@ static int __apply_alternatives_multi_stop(void *unused)
 
 	/* We always have a CPU 0 at this point (__init) */
 	if (smp_processor_id()) {
-		while (!READ_ONCE(all_alternatives_applied))
+		while (!all_alternatives_applied)
 			cpu_relax();
 		isb();
 	} else {
@@ -217,7 +218,7 @@ static int __apply_alternatives_multi_stop(void *unused)
 		BUG_ON(all_alternatives_applied);
 		__apply_alternatives(&region, false, remaining_capabilities);
 		/* Barriers provided by the cache flushing */
-		WRITE_ONCE(all_alternatives_applied, 1);
+		all_alternatives_applied = 1;
 	}
 
 	return 0;
-- 
2.29.1.341.ge80a0c044ae-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: Will Deacon <will@kernel.org>, Kees Cook <keescook@chromium.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org
Subject: [PATCH v4 3/4] arm64: alternatives: Remove READ_ONCE() usage during patch operation
Date: Tue,  3 Nov 2020 12:17:20 +0000	[thread overview]
Message-ID: <20201103121721.5166-4-will@kernel.org> (raw)
In-Reply-To: <20201103121721.5166-1-will@kernel.org>

In preparation for patching the internals of READ_ONCE() itself, replace
its usage on the alternatives patching patch with a volatile variable
instead.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/alternative.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c
index 73039949b5ce..a57cffb752e8 100644
--- a/arch/arm64/kernel/alternative.c
+++ b/arch/arm64/kernel/alternative.c
@@ -21,7 +21,8 @@
 #define ALT_ORIG_PTR(a)		__ALT_PTR(a, orig_offset)
 #define ALT_REPL_PTR(a)		__ALT_PTR(a, alt_offset)
 
-static int all_alternatives_applied;
+/* Volatile, as we may be patching the guts of READ_ONCE() */
+static volatile int all_alternatives_applied;
 
 static DECLARE_BITMAP(applied_alternatives, ARM64_NCAPS);
 
@@ -205,7 +206,7 @@ static int __apply_alternatives_multi_stop(void *unused)
 
 	/* We always have a CPU 0 at this point (__init) */
 	if (smp_processor_id()) {
-		while (!READ_ONCE(all_alternatives_applied))
+		while (!all_alternatives_applied)
 			cpu_relax();
 		isb();
 	} else {
@@ -217,7 +218,7 @@ static int __apply_alternatives_multi_stop(void *unused)
 		BUG_ON(all_alternatives_applied);
 		__apply_alternatives(&region, false, remaining_capabilities);
 		/* Barriers provided by the cache flushing */
-		WRITE_ONCE(all_alternatives_applied, 1);
+		all_alternatives_applied = 1;
 	}
 
 	return 0;
-- 
2.29.1.341.ge80a0c044ae-goog


  parent reply	other threads:[~2020-11-03 12:18 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-03 12:17 [PATCH v4 0/4] Upgrade READ_ONCE() to RCpc acquire on arm64 with LTO Will Deacon
2020-11-03 12:17 ` Will Deacon
2020-11-03 12:17 ` [PATCH v4 1/4] arm64: alternatives: Split up alternative.h Will Deacon
2020-11-03 12:17   ` Will Deacon
2020-11-03 12:40   ` Mark Rutland
2020-11-03 12:40     ` Mark Rutland
2020-11-03 12:42     ` Will Deacon
2020-11-03 12:42       ` Will Deacon
2020-11-03 12:17 ` [PATCH v4 2/4] arm64: cpufeatures: Add capability for LDAPR instruction Will Deacon
2020-11-03 12:17   ` Will Deacon
2020-11-03 12:44   ` Mark Rutland
2020-11-03 12:44     ` Mark Rutland
2020-11-03 12:17 ` Will Deacon [this message]
2020-11-03 12:17   ` [PATCH v4 3/4] arm64: alternatives: Remove READ_ONCE() usage during patch operation Will Deacon
2020-11-03 12:46   ` Mark Rutland
2020-11-03 12:46     ` Mark Rutland
2020-11-03 12:17 ` [PATCH v4 4/4] arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y Will Deacon
2020-11-03 12:17   ` Will Deacon
2020-11-03 12:58   ` Mark Rutland
2020-11-03 12:58     ` Mark Rutland
2020-11-03 13:13     ` Will Deacon
2020-11-03 13:13       ` Will Deacon
2020-11-09 23:25 ` [PATCH v4 0/4] Upgrade READ_ONCE() to RCpc acquire on arm64 with LTO Will Deacon
2020-11-09 23:25   ` Will Deacon

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