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/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 71a39f3..0a490ca 100644
--- 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 void __init ms_hyperv_init_platform(void)
{
+ u64 hv_lapic_frequency;
+
/*
* Extract the features and hints
*/
@@ -76,6 +80,26 @@
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);
}