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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Guo Ren <guoren@linux.alibaba.com>,
        Guo Ren <guoren@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Will Deacon <will@kernel.org>
Subject: [PATCH 4.9 196/218] arm64: patch_text: Fixup last cpu should be master
Date:   Mon, 18 Apr 2022 14:14:22 +0200
Message-Id: <20220418121207.133915106@linuxfoundation.org>
In-Reply-To: <20220418121158.636999985@linuxfoundation.org>
References: <20220418121158.636999985@linuxfoundation.org>
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From: Guo Ren <guoren@linux.alibaba.com>

commit 31a099dbd91e69fcab55eef4be15ed7a8c984918 upstream.

These patch_text implementations are using stop_machine_cpuslocked
infrastructure with atomic cpu_count. The original idea: When the
master CPU patch_text, the others should wait for it. But current
implementation is using the first CPU as master, which couldn't
guarantee the remaining CPUs are waiting. This patch changes the
last CPU as the master to solve the potential risk.

Fixes: ae16480785de ("arm64: introduce interfaces to hotpatch kernel and module code")
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220407073323.743224-2-guoren@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/arm64/kernel/insn.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/arm64/kernel/insn.c
+++ b/arch/arm64/kernel/insn.c
@@ -234,8 +234,8 @@ static int __kprobes aarch64_insn_patch_
 	int i, ret = 0;
 	struct aarch64_insn_patch *pp = arg;
 
-	/* The first CPU becomes master */
-	if (atomic_inc_return(&pp->cpu_count) == 1) {
+	/* The last CPU becomes master */
+	if (atomic_inc_return(&pp->cpu_count) == num_online_cpus()) {
 		for (i = 0; ret == 0 && i < pp->insn_cnt; i++)
 			ret = aarch64_insn_patch_text_nosync(pp->text_addrs[i],
 							     pp->new_insns[i]);