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Date:   Wed, 12 Sep 2018 21:14:48 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Jiri Kosina <jikos@kernel.org>
cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Woodhouse, David" <dwmw@amazon.co.uk>,
        Andi Kleen <ak@linux.intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        "Schaufler, Casey" <casey.schaufler@intel.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH v6 2/3] x86/speculation: Enable cross-hyperthread spectre
 v2 STIBP mitigation
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On Wed, 12 Sep 2018, Jiri Kosina wrote:
>  	case X86_BUG_SPECTRE_V2:
> -		return sprintf(buf, "%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
> +		mutex_lock(&spec_ctrl_mutex);
> +		ret = sprintf(buf, "%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
>  			       boot_cpu_has(X86_FEATURE_USE_IBPB) ? ", IBPB" : "",
>  			       boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "",
> +			       (x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? ", STIBP" : "",
>  			       spectre_v2_module_string());
> +		mutex_unlock(&spec_ctrl_mutex);

The mutex for this printing is overkill. It's a read after all and if there
is a concurrent SMT control fiddling going on then you have a chance of
getting the wrong information as well. I'll zap it.

Thanks,

	tglx