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Commit 9e7827b5 authored by K. Y. Srinivasan's avatar K. Y. Srinivasan Committed by H. Peter Anvin
Browse files

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: default avatarK. Y. Srinivasan <kys@microsoft.com>
Link: http://lkml.kernel.org/r/1380554932-9888-1-git-send-email-olaf@aepfle.de


Tested-by: default avatarOlaf Hering <olaf@aepfle.de>
Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent d0e639c9

arch/x86/include/uapi/asm/hyperv.h

+19 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/cpu/mshyperv.c

+24 −0
Original line number Diff line number Diff line
@@ -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);

}