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

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Message-ID: <16e9b436-5919-39df-3f1a-a717d4229651@codeaurora.org>
Date:   Tue, 11 Aug 2020 10:18:13 +0530
From:   Gaurav Kohli <gkohli@...eaurora.org>
To:     will@...nel.org, linux-arm-kernel@...ts.infradead.org,
        maz@...nel.org, Catalin Marinas <catalin.marinas@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        neeraju@...eaurora.org
Subject: Re: [PATCH] arm64: Skip apply SSBS call for non SSBS system

Hi,

Please let us know, is below patch good to have
or not for non ssbs systems.

On 8/4/2020 7:44 PM, Gaurav Kohli wrote:
> 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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