linux-kernel - Re: [PATCH RFC 2/2] cpu/bugs: cgroup: Add a cgroup knob to bypass CPU mitigations

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Message-ID: <031a122c-f480-4dbc-8022-ca829f4ce500@redhat.com>
Date: Sat, 21 Sep 2024 03:30:07 -0400
From: Waiman Long <longman@...hat.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 David Kaplan <David.Kaplan@....com>,
 Daniel Sneddon <daniel.sneddon@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Steven Rostedt <rostedt@...dmis.org>,
 linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH RFC 2/2] cpu/bugs: cgroup: Add a cgroup knob to bypass CPU
 mitigations

On 9/20/24 03:54, Pawan Gupta wrote:
>>>    static int cpu_local_stat_show(struct seq_file *seq, void *v)
>>>    {
>>>    	struct cgroup __maybe_unused *cgrp = seq_css(seq)->cgroup;
>>> @@ -5290,6 +5326,12 @@ static struct cftype cgroup_base_files[] = {
>>>    		.name = "cpu.stat.local",
>>>    		.seq_show = cpu_local_stat_show,
>>>    	},
>>> +	{
>>> +		.name = "cpu.skip_mitigation",
>>> +		.flags = CFTYPE_NOT_ON_ROOT,
>>> +		.seq_show = cpu_skip_mitigation_show,
>>> +		.write = cgroup_skip_mitigation_write,
>>> +	},
>>>    	{ }	/* terminate */
>>>    };
>> Since this control knob is effective only for x86_64, should we enable this
>> only for this architecture?
> This should be under a CONFIG option that depends on the architecture
> selected. I don't see a reason why it will not be useful for other archs.

Using a CONFIG option looks fine to me. I just want to make sure that 
arches that don't support it won't have a useless control knob show up.

Cheers,
Longman