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SubjectRe: [PATCH 2/2] x86/xen: use capabilities instead of fake cpuid values
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On 17/02/17 15:05, Boris Ostrovsky wrote:
>
>
> 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@suse.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?

Yes. But this shouldn't be a problem as the kernel is always testing
X86_FEATURE_APERFMPERF for testing the support.

>> 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().

Okay. I'll move them.

I think we can convert some of the remaining cpuid bit modifications to
cpu capabilities as well.


Juergen

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