linux-kernel - Re: [PATCH 2/2] x86/xen: use capabilities instead of fake cpuid values

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Date:   Fri, 17 Feb 2017 09:05:09 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org, x86@...nel.org
Cc:     hpa@...or.com, tglx@...utronix.de, mingo@...hat.com
Subject: Re: [PATCH 2/2] x86/xen: use capabilities instead of fake cpuid
 values



On 02/17/2017 02:36 AM, Juergen Gross wrote:
> When running as pv domain xen_cpuid() is being used instead of
> native_cpuid(). In xen_cpuid() the aperf/mperf feature is indicated
> as not being present by special casing the related cpuid leaf.
>
> Instead of delivering fake cpuid values clear the cpu capability bit
> for aperf/mperf instead.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  arch/x86/xen/enlighten.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index 83399ce..0eebb75 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -301,9 +301,6 @@ xen_running_on_version_or_later(unsigned int major, unsigned int minor)
>  	return false;
>  }
>
> -#define CPUID_THERM_POWER_LEAF 6
> -#define APERFMPERF_PRESENT 0
> -
>  static __read_mostly unsigned int cpuid_leaf1_edx_mask = ~0;
>  static __read_mostly unsigned int cpuid_leaf1_ecx_mask = ~0;
>
> @@ -337,11 +334,6 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
>  		*dx = cpuid_leaf5_edx_val;
>  		return;
>
> -	case CPUID_THERM_POWER_LEAF:
> -		/* Disabling APERFMPERF for kernel usage */
> -		maskecx = ~(1 << APERFMPERF_PRESENT);
> -		break;
> -


But now APERF/MPERF will be reported as supported by CPUID, won't it?


>  	case 0xb:
>  		/* Suppress extended topology stuff */
>  		maskebx = 0;
> @@ -462,6 +454,9 @@ static void __init xen_init_cpuid_mask(void)
>  	if (xen_check_mwait())
>  		cpuid_leaf1_ecx_set_mask = (1 << (X86_FEATURE_MWAIT % 32));
>
> +	/* Disable APERFMPERF feature. */
> +	setup_clear_cpu_cap(X86_FEATURE_APERFMPERF);
> +
>  	/* Disable DCA feature. */
>  	setup_clear_cpu_cap(X86_FEATURE_DCA);


I think both of those can go to xen_set_cpu_features().

-boris