x86/hyperv: Read TSC frequency from a synthetic MSR

It was found that SMI_TRESHOLD of 50000 is not enough for Hyper-V
guests in nested environment and falling back to counting jiffies
is not an option for Gen2 guests as they don't have PIT. As Hyper-V
provides TSC frequency in a synthetic MSR we can just use this information
instead of doing a error prone calibration.

Reported-and-tested-by: Ladi Prosek <lprosek@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Jork Loeser <jloeser@microsoft.com>
Cc: devel@linuxdriverproject.org
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Link: http://lkml.kernel.org/r/20170622100730.18112-3-vkuznets@redhat.com

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 3563c8e6c01404559391976e37ba7921fa571ab2..70e717fccdd6cabaf8eb778b6f407c43b6e0c412 100644 (file)
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -161,6 +161,15 @@ static int hv_nmi_unknown(unsigned int val, struct pt_regs *regs)
 }
 #endif
 
+static unsigned long hv_get_tsc_khz(void)
+{
+       unsigned long freq;
+
+       rdmsrl(HV_X64_MSR_TSC_FREQUENCY, freq);
+
+       return freq / 1000;
+}
+
 static void __init ms_hyperv_init_platform(void)
 {
        int hv_host_info_eax;
@@ -193,6 +202,12 @@ static void __init ms_hyperv_init_platform(void)
                        hv_host_info_edx >> 24, hv_host_info_edx & 0xFFFFFF);
        }
 
+       if (ms_hyperv.features & HV_X64_ACCESS_FREQUENCY_MSRS &&
+           ms_hyperv.misc_features & HV_FEATURE_FREQUENCY_MSRS_AVAILABLE) {
+               x86_platform.calibrate_tsc = hv_get_tsc_khz;
+               x86_platform.calibrate_cpu = hv_get_tsc_khz;
+       }
+
 #ifdef CONFIG_X86_LOCAL_APIC
        if (ms_hyperv.features & HV_X64_ACCESS_FREQUENCY_MSRS &&
            ms_hyperv.misc_features & HV_FEATURE_FREQUENCY_MSRS_AVAILABLE) {