Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 21 Jun 2023 22:40:53 -0700
From:   Josh Poimboeuf <jpoimboe@kernel.org>
To:     Waiman Long <longman@redhat.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        Len Brown <lenb@kernel.org>, linux-kernel@vger.kernel.org,
        x86@kernel.org, linux-pm@vger.kernel.org,
        Robin Jarry <rjarry@redhat.com>, Joe Mario <jmario@redhat.com>
Subject: Re: [PATCH v3 1/3] x86/idle: Disable IBRS when cpu is offline
Message-ID: <20230622054053.uy577qezu5a65buc@treble>
References: <20230622003603.1188364-1-longman@redhat.com>
 <20230622003603.1188364-2-longman@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20230622003603.1188364-2-longman@redhat.com>
Precedence: bulk

On Wed, Jun 21, 2023 at 08:36:01PM -0400, Waiman Long wrote:
> +/*
> + * naitve_play_dead() is essentially a __noreturn function, but it can't
> + * be marked as such as the compiler may complain about it.
> + */

FWIW, we could in theory do so by marking the smp_ops.play_dead function
pointer as __noreturn, but it would be tricky to teach objtool how to
understand that.

>  void native_play_dead(void)
>  {
> +	if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS)) {
> +		this_cpu_write(x86_spec_ctrl_current, 0);
> +		native_wrmsrl(MSR_IA32_SPEC_CTRL, 0);
> +	}

Can update_spec_ctrl() be used instead?

-- 
Josh