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SubjectRe: [PATCH v5 3/3] x86/bugs: Add 'spectre_bhi=vmexit' cmdline option
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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>

>

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