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Re: [Xen-devel] [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@xxxxxxxx>
---
 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

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