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

[Josh Poimboeuf]

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().

-- 
Josh