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

[Nikolay Borisov]

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@xxxxxxxx>

>