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Date: Fri, 17 Feb 2017 09:30:57 -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 09:19 AM, Juergen Gross wrote: > 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@...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? > > Yes. But this shouldn't be a problem as the kernel is always testing > X86_FEATURE_APERFMPERF for testing the support. But X86_FEATURE_APERFMPERF cap is set based on CPUID query. -boris > >>> 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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