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

From: Thomas Gleixner <tglx@linutronix.de>
To: Fenghua Yu <fenghua.yu@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	H Peter Anvin <hpa@zytor.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ravi V Shankar <ravi.v.shankar@intel.com>,
	Xiaoyao Li <xiaoyao.li@intel.com>,
	Christopherson Sean J <sean.j.christopherson@intel.com>,
	Kalle Valo <kvalo@codeaurora.org>,
	Michael Chan <michael.chan@broadcom.com>,
	linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>,
	kvm@vger.kernel.org, netdev@vger.kernel.org,
	linux-wireless@vger.kernel.org
Subject: Re: [PATCH v8 10/15] x86/split_lock: Handle #AC exception for split lock
Date: Thu, 25 Apr 2019 09:29:17 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1904250927140.1762@nanos.tec.linutronix.de> (raw)
In-Reply-To: <1556134382-58814-11-git-send-email-fenghua.yu@intel.com>

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