x86, hyperv: Get the local APIC timer frequency from the hypervisor

Hyper-V supports a mechanism for retrieving the local APIC frequency.
Use this and bypass the calibration code in the kernel . This would
allow us to boot the Linux kernel as a "modern VM" on Hyper-V where
many of the legacy devices (such as PIT) are not emulated.

I would like to thank Olaf Hering <olaf@aepfle.de>, Jan Beulich <JBeulich@suse.com> and
H. Peter Anvin <h.peter.anvin@intel.com> for their help in this effort.

In this version of the patch, I have addressed Jan's comments.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Link: http://lkml.kernel.org/r/1380554932-9888-1-git-send-email-olaf@aepfle.de
Tested-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

diff --git a/arch/x86/include/uapi/asm/hyperv.h b/arch/x86/include/uapi/asm/hyperv.h
index b80420b..b8f1c01 100644 (file)
--- a/arch/x86/include/uapi/asm/hyperv.h
+++ b/arch/x86/include/uapi/asm/hyperv.h
@@ -27,6 +27,19 @@
 #define HV_X64_MSR_VP_RUNTIME_AVAILABLE                (1 << 0)
 /* Partition Reference Counter (HV_X64_MSR_TIME_REF_COUNT) available*/
 #define HV_X64_MSR_TIME_REF_COUNT_AVAILABLE    (1 << 1)
+
+/*
+ * There is a single feature flag that signifies the presence of the MSR
+ * that can be used to retrieve both the local APIC Timer frequency as
+ * well as the TSC frequency.
+ */
+
+/* Local APIC timer frequency MSR (HV_X64_MSR_APIC_FREQUENCY) is available */
+#define HV_X64_MSR_APIC_FREQUENCY_AVAILABLE (1 << 11)
+
+/* TSC frequency MSR (HV_X64_MSR_TSC_FREQUENCY) is available */
+#define HV_X64_MSR_TSC_FREQUENCY_AVAILABLE (1 << 11)
+
 /*
  * Basic SynIC MSRs (HV_X64_MSR_SCONTROL through HV_X64_MSR_EOM
  * and HV_X64_MSR_SINT0 through HV_X64_MSR_SINT15) available
@@ -136,6 +149,12 @@
 /* MSR used to read the per-partition time reference counter */
 #define HV_X64_MSR_TIME_REF_COUNT              0x40000020
 
+/* MSR used to retrieve the TSC frequency */
+#define HV_X64_MSR_TSC_FREQUENCY               0x40000022
+
+/* MSR used to retrieve the local APIC timer frequency */
+#define HV_X64_MSR_APIC_FREQUENCY              0x40000023
+
 /* Define the virtual APIC registers */
 #define HV_X64_MSR_EOI                         0x40000070
 #define HV_X64_MSR_ICR                         0x40000071

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 71a39f3..0a490ca 100644 (file)
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -15,6 +15,7 @@
 #include <linux/clocksource.h>
 #include <linux/module.h>
 #include <linux/hardirq.h>
+#include <linux/efi.h>
 #include <linux/interrupt.h>
 #include <asm/processor.h>
 #include <asm/hypervisor.h>
@@ -23,6 +24,7 @@
 #include <asm/desc.h>
 #include <asm/idle.h>
 #include <asm/irq_regs.h>
+#include <asm/i8259.h>
 
 struct ms_hyperv_info ms_hyperv;
 EXPORT_SYMBOL_GPL(ms_hyperv);
@@ -67,6 +69,8 @@ static struct clocksource hyperv_cs = {
 
 static void __init ms_hyperv_init_platform(void)
 {
+       u64     hv_lapic_frequency;
+
        /*
         * Extract the features and hints
         */
@@ -76,6 +80,26 @@ static void __init ms_hyperv_init_platform(void)
        printk(KERN_INFO "HyperV: features 0x%x, hints 0x%x\n",
               ms_hyperv.features, ms_hyperv.hints);
 
+       if (ms_hyperv.features & HV_X64_MSR_APIC_FREQUENCY_AVAILABLE) {
+               /*
+                * Get the APIC frequency.
+                */
+               rdmsrl(HV_X64_MSR_APIC_FREQUENCY, hv_lapic_frequency);
+               hv_lapic_frequency = div_u64(hv_lapic_frequency, HZ);
+               lapic_timer_frequency = hv_lapic_frequency;
+               printk(KERN_INFO "HyperV: LAPIC Timer Frequency: %#x\n",
+                               lapic_timer_frequency);
+
+               /*
+                * On Hyper-V, when we are booting off an EFI firmware stack,
+                * we do not have many legacy devices including PIC, PIT etc.
+                */
+               if (efi_enabled(EFI_BOOT)) {
+                       printk(KERN_INFO "HyperV: Using null_legacy_pic\n");
+                       legacy_pic = &null_legacy_pic;
+               }
+       }
+
        if (ms_hyperv.features & HV_X64_MSR_TIME_REF_COUNT_AVAILABLE)
                clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100);
 }