linux-kernel - Re: [PATCH v17] x86/split_lock: Enable split lock detection by kernel

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Message-ID: <87d0b24f6r.fsf@nanos.tec.linutronix.de>
Date:   Wed, 29 Jan 2020 13:31:24 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Luck\, Tony" <tony.luck@...el.com>
Cc:     Mark D Rustad <mrustad@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        "Christopherson\, Sean J" <sean.j.christopherson@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Yu\, Fenghua" <fenghua.yu@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        "Raj\, Ashok" <ashok.raj@...el.com>,
        "Shankar\, Ravi V" <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v17] x86/split_lock: Enable split lock detection by kernel

"Luck, Tony" <tony.luck@...el.com> writes:
> +static bool __sld_msr_set(bool on)
> +{
> +	u64 test_ctrl_val;
> +
> +	if (rdmsrl_safe(MSR_TEST_CTRL, &test_ctrl_val))
> +		return false;
> +
> +	if (on)
> +		test_ctrl_val |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
> +	else
> +		test_ctrl_val &= ~MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
> +
> +	return !wrmsrl_safe(MSR_TEST_CTRL, test_ctrl_val);
> +}
> +
> +static void split_lock_init(void)
> +{
> +	if (sld_state == sld_off)
> +		return;
> +
> +	if (__sld_msr_set(true))
> +		return;
> +
> +	/*
> +	 * If this is anything other than the boot-cpu, you've done
> +	 * funny things and you get to keep whatever pieces.
> +	 */
> +	pr_warn("MSR fail -- disabled\n");
> +	__sld_msr_set(sld_off);

This one is pretty pointless. If the rdmsrl or the wrmsrl failed, then
the next attempt is going to fail too. Aside of that sld_off would be not
really the right argument value here. I just zap that line.

Thanks,

        tglx