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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Luck\, Tony" <tony.luck@intel.com>
Cc:     Mark D Rustad <mrustad@gmail.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        "Christopherson\, Sean J" <sean.j.christopherson@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Yu\, Fenghua" <fenghua.yu@intel.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        H Peter Anvin <hpa@zytor.com>,
        "Raj\, Ashok" <ashok.raj@intel.com>,
        "Shankar\, Ravi V" <ravi.v.shankar@intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Subject: Re: [PATCH v17] x86/split_lock: Enable split lock detection by kernel
In-Reply-To: <20200126200535.GB30377@agluck-desk2.amr.corp.intel.com>
References: <4E95BFAA-A115-4159-AA4F-6AAB548C6E6C@gmail.com> <C3302B2F-177F-4C39-910E-EADBA9285DD0@intel.com> <8CC9FBA7-D464-4E58-8912-3E14A751D243@gmail.com> <20200126200535.GB30377@agluck-desk2.amr.corp.intel.com>
Date:   Wed, 29 Jan 2020 13:31:24 +0100
Message-ID: <87d0b24f6r.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

"Luck, Tony" <tony.luck@intel.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