Re: [PATCH v3 06/18] x86/spec-ctrl: introduce Address Space Isolation command line option

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.10.2026 12:40, George Dunlap wrote:
> --- a/xen/arch/x86/spec_ctrl.c
> +++ b/xen/arch/x86/spec_ctrl.c
> @@ -86,6 +86,13 @@ bool __ro_after_init opt_bp_spec_reduce = true;
>  
>  static bool __initdata opt_ibpb_alt;
>  
> +/*
> + * Give each vCPU of an HVM domain its own per-domain area (vCPU-PT).  Off by
> + * default until the feature is complete.
> + */
> +bool __ro_after_init opt_vcpu_pt_hvm;
> +bool __ro_after_init opt_vcpu_pt_hwdom;

I'm a little worried of this name, which doesn't distinguish PV and PVH. Yes,
the variable name is already long-ish, yet I think inserting "pvh" is going
to help.

> @@ -487,6 +494,62 @@ static int __init cf_check parse_pv_l1tf(const char *s)
>  }
>  custom_param("pv-l1tf", parse_pv_l1tf);
>  
> +static int __init cf_check parse_asi(const char *s)
> +{
> +    const char *ss;
> +    int val, rc = 0;
> +
> +    /* Interpret 'asi' alone in its positive boolean form. */
> +    if ( *s == '\0' )
> +        opt_vcpu_pt_hwdom = opt_vcpu_pt_hvm = true;
> +
> +    do {
> +        ss = strchr(s, ',');
> +        if ( !ss )
> +            ss = strchr(s, '\0');
> +
> +        val = parse_bool(s, ss);
> +        switch ( val )
> +        {
> +        case 0:
> +        case 1:
> +            opt_vcpu_pt_hwdom = opt_vcpu_pt_hvm = val;
> +            break;
> +
> +        default:
> +            if ( (val = parse_boolean("hvm", s, ss)) >= 0 )
> +                opt_vcpu_pt_hvm = val;
> +            else if ( (val = parse_boolean("vcpu-pt", s, ss)) != -1 )
> +            {
> +                switch ( val )
> +                {
> +                case 1:
> +                case 0:
> +                    opt_vcpu_pt_hwdom = opt_vcpu_pt_hvm = val;
> +                    break;
> +
> +                case -2:
> +                    s += strlen("vcpu-pt=");
> +                    if ( (val = parse_boolean("hvm", s, ss)) >= 0 )
> +                        opt_vcpu_pt_hvm = val;
> +                    else
> +                default:
> +                        rc = -EINVAL;
> +                    break;

While personally I like the reduced redundancy from placing case labels
like the default: one here, Misra rule 16.2 wants us to not use such.
Note that as written there's no violation, yet iirc Andrew keeps asking
for figure braces in such constructs. I think we're better off not
introducing new instances (the rule is marked clean, so with the braces
added we simply can't, unless the file is excluded from scanning).

Jan