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Message-ID: <309d15f5-0dd8-aee8-14a6-621a071bc363@redhat.com>
Date:   Wed, 21 Jun 2023 10:51:33 -0400
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Subject: Re: [PATCH v2 2/5] x86/idle: Disable IBRS when cpu is offline
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To:     Peter Zijlstra <peterz@infradead.org>
Cc:     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>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        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>
References: <20230620140625.1001886-1-longman@redhat.com>
 <20230620140625.1001886-3-longman@redhat.com>
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 <5cb81f3b-45a0-d566-3d63-569b5706e9fe@redhat.com>
 <20230621144848.GJ2053369@hirez.programming.kicks-ass.net>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <20230621144848.GJ2053369@hirez.programming.kicks-ass.net>
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On 6/21/23 10:48, Peter Zijlstra wrote:
> On Wed, Jun 21, 2023 at 10:44:23AM -0400, Waiman Long wrote:
>
>> Well, hlt_play_dead() is only called if cpuidle_play_dead() returns an error
>> which is not the typical case. My testing does confirm that this patch is
>> able to keep the IBRS bit off when a CPU is offline via its online sysfs
>> file.
> The point is; your re-enable IBRS hunk at the end is dead-code. It
> should never ever run and having it is confusing.

What I meant is that hlt_play_dead() should never be called unless there 
is some serious problem with the system and native_play_dead() does 
return in normal usage.

Cheers,
Longman