Received-SPF: pass (google.com: domain of linux-kernel+bounces-174283-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Message-ID: <60ddec81-5102-4984-848a-ae3adb8c4c38@suse.com>
Date: Thu, 9 May 2024 11:21:44 +0300
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v5 3/3] x86/bugs: Add 'spectre_bhi=vmexit' cmdline option
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
 Linus Torvalds <torvalds@linux-foundation.org>,
 Daniel Sneddon <daniel.sneddon@linux.intel.com>,
 Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
 Thomas Gleixner <tglx@linutronix.de>,
 Alexandre Chartre <alexandre.chartre@oracle.com>,
 Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
 Peter Zijlstra <peterz@infradead.org>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Sean Christopherson <seanjc@google.com>,
 Andrew Cooper <andrew.cooper3@citrix.com>,
 Dave Hansen <dave.hansen@linux.intel.com>, KP Singh <kpsingh@kernel.org>,
 Waiman Long <longman@redhat.com>, Borislav Petkov <bp@alien8.de>,
 Ingo Molnar <mingo@kernel.org>, Maksim Davydov <davydov-max@yandex-team.ru>
References: <cover.1715059256.git.jpoimboe@kernel.org>
 <66327dcf87284a09ed17ac24227695ea3ba1f287.1715059256.git.jpoimboe@kernel.org>
 <f48601e1-e8a6-4161-9a77-32ad10c887de@suse.com>
 <20240509052447.kwdlruqad7r5h4pi@treble>
From: Nikolay Borisov <nik.borisov@suse.com>
Content-Language: en-US
In-Reply-To: <20240509052447.kwdlruqad7r5h4pi@treble>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit


On 9.05.24 г. 8:24 ч., Josh Poimboeuf wrote:
> On Wed, May 08, 2024 at 06:10:21PM +0300, Nikolay Borisov wrote:
>>> @@ -1659,19 +1662,22 @@ static void __init bhi_select_mitigation(void)
>>>    			return;
>>>    	}
>>> +	/* Mitigate in hardware if supported */
>>>    	if (spec_ctrl_bhi_dis())
>>>    		return;
>>>    	if (!IS_ENABLED(CONFIG_X86_64))
>>>    		return;
>>> -	/* Mitigate KVM by default */
>>> -	setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT);
>>> -	pr_info("Spectre BHI mitigation: SW BHB clearing on vm exit\n");
>>> +	if (bhi_mitigation == BHI_MITIGATION_VMEXIT_ONLY) {
>>> +		pr_info("Spectre BHI mitigation: SW BHB clearing on vm exit only\n");
>>> +		setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT);
>>> +		return;
>>> +	}
>>
>> nit: How about setting CLEAR_BHB_LOOP_ON_VMEXIT unconditionally, then
>> afterwards checking if MITIGATION_VMEXIT_ONLY is set and if yes simply
>> return, that way you don't duplicate the setup of the VMEXIT code
> 
> I think the duplication actually makes it more readable.  In both cases
> it puts the setting of the features together along with the
> corresponding pr_info().

Right, my suggestion also meant that setting + pr info will be together, 
unconditional and if MITIGATION_VMEXIT_ONLY is set we return early, 
without setting X86_FEATURE_CLEAR_BHB_LOOP. In any case it's a minor 
remark, feel free to ignore.

Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>

>