Re: [Xen-devel] [PATCH v2 1/3] x86/vpmu: Add get/put_vpmu() and VPMU_AVAILABLE

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 17/02/17 17:40, Boris Ostrovsky wrote:
> @@ -509,15 +498,63 @@ void vpmu_initialise(struct vcpu *v)
>      if ( ret )
>          printk(XENLOG_G_WARNING "VPMU: Initialization failed for %pv\n", v);
>  
> -    /* Intel needs to initialize VPMU ops even if VPMU is not in use */
> -    if ( !is_priv_vpmu &&
> -         (ret || (vpmu_mode == XENPMU_MODE_OFF) ||
> -          (vpmu_mode == XENPMU_MODE_ALL)) )
> +    return ret;
> +}
> +
> +static void get_vpmu(struct vcpu *v)
> +{
> +    spin_lock(&vpmu_lock);
> +
> +    /*
> +     * Count active VPMUs so that we won't try to change vpmu_mode while
> +     * they are in use.
> +     * vpmu_mode can be safely updated while dom0's VPMUs are active and
> +     * so we don't need to include it in the count.
> +     */
> +    if ( !is_hardware_domain(v->domain) &&
> +        (vpmu_mode & (XENPMU_MODE_SELF | XENPMU_MODE_HV)) )
> +    {
> +        vpmu_count++;
> +        vpmu_set(vcpu_vpmu(v), VPMU_AVAILABLE);
> +    }
> +    else if ( is_hardware_domain(v->domain) &&
> +              (vpmu_mode != XENPMU_MODE_OFF) )
> +        vpmu_set(vcpu_vpmu(v), VPMU_AVAILABLE);

Why do we recalculate AVAILABLE on every get()?

(In the absence of toolstack control from the CPUID side), surely it
should be set (or not) exactly once during domain creation, and be
unchanged thereafter?

~Andrew

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