linux-kernel - [PATCH] arm64: Skip apply SSBS call for non SSBS system

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Date:   Tue,  4 Aug 2020 19:44:42 +0530
From:   Gaurav Kohli <gkohli@...eaurora.org>
To:     will@...nel.org, linux-arm-kernel@...ts.infradead.org,
        maz@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        neeraju@...eaurora.org, Gaurav Kohli <gkohli@...eaurora.org>
Subject: [PATCH] arm64: Skip apply SSBS call for non SSBS system

In a system where no cpu's implement SSBS, for
them no need to set pstate. This might help to save
few cpu cycles during context switch.

Signed-off-by: Gaurav Kohli <gkohli@...eaurora.org>

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 6089638..79f80f1 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -477,6 +477,13 @@ static void ssbs_thread_switch(struct task_struct *next)
 	struct pt_regs *regs = task_pt_regs(next);
 
 	/*
+	 * For Targets which don't have SSBS support, they
+	 * can return from here.
+	 */
+	if (!IS_ENABLED(CONFIG_ARM64_SSBD))
+		return;
+
+	/*
 	 * Nothing to do for kernel threads, but 'regs' may be junk
 	 * (e.g. idle task) so check the flags and bail early.
 	 */
-- 
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