Re: [PATCH V2 1/1] X86: Hyper-V: Get the local APIC timer frequencyfrom the hypervisor

[Gleb Natapov]

On Tue, Sep 03, 2013 at 11:30:23AM -0700, K. Y. Srinivasan wrote:
> 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@xxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx> and
> H. Peter Anvin <h.peter.anvin@xxxxxxxxx> 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@xxxxxxxxxxxxx>
> ---
>  arch/x86/include/uapi/asm/hyperv.h |   19 +++++++++++++++++++
>  arch/x86/kernel/cpu/mshyperv.c     |   24 ++++++++++++++++++++++++
>  2 files changed, 43 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/include/uapi/asm/hyperv.h b/arch/x86/include/uapi/asm/hyperv.h
> index b80420b..b8f1c01 100644
> --- 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
> +
You do not use this MSR in the patch, but in general how it suppose to
work during migration if host TSC frequency changes?

> +/* 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..b3dc639 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 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 /= 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);
>  }
> -- 
> 1.7.4.1
> 
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--
			Gleb.
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