linux-kernel - Re: [PATCH v8 10/15] x86/split_lock: Handle #AC exception for split lock

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Message-ID: <alpine.DEB.2.21.1904250927140.1762@nanos.tec.linutronix.de>
Date:   Thu, 25 Apr 2019 09:29:17 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
cc:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Christopherson Sean J <sean.j.christopherson@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Michael Chan <michael.chan@...adcom.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, kvm@...r.kernel.org,
        netdev@...r.kernel.org, linux-wireless@...r.kernel.org
Subject: Re: [PATCH v8 10/15] x86/split_lock: Handle #AC exception for split
 lock

On Wed, 24 Apr 2019, Fenghua Yu wrote:

> +void handle_split_lock_kernel_mode(void)

....

> +dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code)
> +{
> +	unsigned int trapnr = X86_TRAP_AC;
> +	char str[] = "alignment check";
> +	int signr = SIGBUS;
> +
> +	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
> +
> +	if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) ==
> +		       NOTIFY_STOP)
> +		return;
> +
> +	cond_local_irq_enable(regs);
> +	if (!user_mode(regs) &&
> +	    static_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT)) {
> +		/*
> +		 * Only split lock can generate #AC from kernel at this point.
> +		 * Warn and disable split lock detection on this CPU. The
> +		 * faulting instruction will be executed without generating
> +		 * another #AC fault.
> +		 */
> +		return handle_split_lock_kernel_mode();

return fun()? For some reason gcc will not complain about that, but for the
reader it's confusing at best.

Thanks,

	tglx