linux-kernel - Re: [PATCH v4 2/4] x86: simplify _TIF_SYSCALL

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Message-ID: <20190603172251.GG63283@arrakis.emea.arm.com>
Date:   Mon, 3 Jun 2019 18:22:52 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Sudeep Holla <sudeep.holla@....com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Will Deacon <will.deacon@....com>,
        Oleg Nesterov <oleg@...hat.com>,
        Richard Weinberger <richard@....at>, jdike@...toit.com,
        Steve Capper <Steve.Capper@....com>,
        Haibo Xu <haibo.xu@....com>, Bin Lu <bin.lu@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v4 2/4] x86: simplify _TIF_SYSCALL_EMU handling

On Thu, May 23, 2019 at 10:06:16AM +0100, Sudeep Holla wrote:
> The usage of emulated/_TIF_SYSCALL_EMU flags in syscall_trace_enter
> seems to be bit overcomplicated than required. Let's simplify it.
> 
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Acked-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  arch/x86/entry/common.c | 17 ++++++-----------
>  1 file changed, 6 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
> index a986b3c8294c..0a61705d62ec 100644
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -72,23 +72,18 @@ static long syscall_trace_enter(struct pt_regs *regs)
>  
>  	struct thread_info *ti = current_thread_info();
>  	unsigned long ret = 0;
> -	bool emulated = false;
>  	u32 work;
>  
>  	if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
>  		BUG_ON(regs != task_pt_regs(current));
>  
> -	work = READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
> +	work = READ_ONCE(ti->flags);
>  
> -	if (unlikely(work & _TIF_SYSCALL_EMU))
> -		emulated = true;
> -
> -	if ((emulated || (work & _TIF_SYSCALL_TRACE)) &&
> -	    tracehook_report_syscall_entry(regs))
> -		return -1L;
> -
> -	if (emulated)
> -		return -1L;
> +	if (work & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU)) {
> +		ret = tracehook_report_syscall_entry(regs);
> +		if (ret || (work & _TIF_SYSCALL_EMU))
> +			return -1L;
> +	}

Andy (or the other x86 folk), could I please get an ack on this patch? I
plan to queue this series through the arm64 tree (though if you want to
merge it separately, it looks like an independent clean-up with no
dependencies on the other patches).

Thanks.

-- 
Catalin