Re: [RFC PATCH v2 1/2] add support for Hyper-V reference time counter

[Vadim Rozenfeld <vrozenfe@redhat.com>]

----- Original Message -----
From: "Marcelo Tosatti" <mtosatti@redhat.com>
To: "Vadim Rozenfeld" <vrozenfe@redhat.com>
Cc: kvm@vger.kernel.org, gleb@redhat.com, pl@dlh.net
Sent: Wednesday, May 22, 2013 10:46:14 AM
Subject: Re: [RFC PATCH v2 1/2] add support for Hyper-V reference time counter

On Sun, May 19, 2013 at 05:06:36PM +1000, Vadim Rozenfeld wrote:
> Signed-off: Peter Lieven <pl@dlh.net>
> Signed-off: Gleb Natapov <gleb@redhat.com>
> Signed-off: Vadim Rozenfeld <vrozenfe@redhat.com>
> 
> v1 -> v2
> 1. mark TSC page dirty as suggested by 
>     Eric Northup <digitaleric@google.com> and Gleb
> 2. disable local irq when calling get_kernel_ns, 
>     as it was done by Peter Lieven <pl@dlhnet.de>
> 3. move check for TSC page enable from second patch
>     to this one.
>  
> ---
>  arch/x86/include/asm/kvm_host.h    |  2 ++
>  arch/x86/include/uapi/asm/hyperv.h | 14 ++++++++++++++
>  arch/x86/kvm/x86.c                 | 39 +++++++++++++++++++++++++++++++++++++-
>  include/uapi/linux/kvm.h           |  1 +
>  4 files changed, 55 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 3741c65..f0fee35 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -575,6 +575,8 @@ struct kvm_arch {
>  	/* fields used by HYPER-V emulation */
>  	u64 hv_guest_os_id;
>  	u64 hv_hypercall;
> +	u64 hv_ref_count;
> +	u64 hv_tsc_page;
>  
>  	#ifdef CONFIG_KVM_MMU_AUDIT
>  	int audit_point;
> diff --git a/arch/x86/include/uapi/asm/hyperv.h b/arch/x86/include/uapi/asm/hyperv.h
> index b80420b..890dfc3 100644
> --- a/arch/x86/include/uapi/asm/hyperv.h
> +++ b/arch/x86/include/uapi/asm/hyperv.h
> @@ -136,6 +136,9 @@
>  /* MSR used to read the per-partition time reference counter */
>  #define HV_X64_MSR_TIME_REF_COUNT		0x40000020
>  
> +/* A partition's reference time stamp counter (TSC) page */
> +#define HV_X64_MSR_REFERENCE_TSC		0x40000021
> +
>  /* Define the virtual APIC registers */
>  #define HV_X64_MSR_EOI				0x40000070
>  #define HV_X64_MSR_ICR				0x40000071
> @@ -179,6 +182,9 @@
>  #define HV_X64_MSR_APIC_ASSIST_PAGE_ADDRESS_MASK	\
>  		(~((1ull << HV_X64_MSR_APIC_ASSIST_PAGE_ADDRESS_SHIFT) - 1))
>  
> +#define HV_X64_MSR_TSC_REFERENCE_ENABLE			0x00000001
> +#define HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT	12
> +
>  #define HV_PROCESSOR_POWER_STATE_C0		0
>  #define HV_PROCESSOR_POWER_STATE_C1		1
>  #define HV_PROCESSOR_POWER_STATE_C2		2
> @@ -191,4 +197,12 @@
>  #define HV_STATUS_INVALID_ALIGNMENT		4
>  #define HV_STATUS_INSUFFICIENT_BUFFERS		19
>  
> +typedef struct _HV_REFERENCE_TSC_PAGE {
> +	__u32 TscSequence;
> +	__u32 Rserved1;
> +	__u64 TscScale;
> +	__s64  TscOffset;
> +} HV_REFERENCE_TSC_PAGE, *PHV_REFERENCE_TSC_PAGE;
> +
> +
>  #endif
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8d28810..9645dab 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -843,7 +843,7 @@ EXPORT_SYMBOL_GPL(kvm_rdpmc);
>  static u32 msrs_to_save[] = {
>  	MSR_KVM_SYSTEM_TIME, MSR_KVM_WALL_CLOCK,
>  	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW, not needed.
> -	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
> +	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL, HV_X64_MSR_TIME_REF_COUNT,
>  	HV_X64_MSR_APIC_ASSIST_PAGE, MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
>  	MSR_KVM_PV_EOI_EN,
>  	MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
> @@ -1788,6 +1788,8 @@ static bool kvm_hv_msr_partition_wide(u32 msr)
>  	switch (msr) {
>  	case HV_X64_MSR_GUEST_OS_ID:
>  	case HV_X64_MSR_HYPERCALL:
> +	case HV_X64_MSR_REFERENCE_TSC:
> +	case HV_X64_MSR_TIME_REF_COUNT:
>  		r = true;
>  		break;
>  	}
> @@ -1827,6 +1829,29 @@ static int set_msr_hyperv_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data)
>  		if (__copy_to_user((void __user *)addr, instructions, 4))
>  			return 1;
>  		kvm->arch.hv_hypercall = data;
> +		local_irq_disable();
> +		kvm->arch.hv_ref_count = get_kernel_ns();
> +		local_irq_enable();
> +		break;

local_irq_disable/local_irq_enable not needed.


What is the reasoning behind reading this time value at msr write time?
[VR] Windows writs this MSR only once, during HAL initialization.
So, I decided to treat this call as a partition crate event.

> +	}
> +	case HV_X64_MSR_REFERENCE_TSC: {
> +		u64 gfn;
> +		unsigned long addr;
> +		HV_REFERENCE_TSC_PAGE tsc_ref;
> +		tsc_ref.TscSequence = 0;
> +		if (!(data & HV_X64_MSR_TSC_REFERENCE_ENABLE)) {
> +			kvm->arch.hv_tsc_page = data;
> +			break;
> +		}
> +		gfn = data >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;
> +		addr = gfn_to_hva(kvm, data >>
> +				HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT);
> +		if (kvm_is_error_hva(addr))
> +			return 1;
> +		if (__copy_to_user((void __user *)addr, &tsc_ref, sizeof(tsc_ref)))
> +			return 1;
> +		mark_page_dirty(kvm, gfn);
> +		kvm->arch.hv_tsc_page = data;
>  		break;
>  	}
>  	default:
> @@ -2253,6 +2278,17 @@ static int get_msr_hyperv_pw(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
>  	case HV_X64_MSR_HYPERCALL:
>  		data = kvm->arch.hv_hypercall;
>  		break;
> +	case HV_X64_MSR_TIME_REF_COUNT: {
> +		u64 now_ns;
> +		local_irq_disable();
> +		now_ns = get_kernel_ns() + kvm->arch.kvmclock_offset;
> +		data = div_u64(now_ns - kvm->arch.hv_ref_count, 100);
> +		local_irq_enable();
> +		break;
> +	}

local_irq_disable/enable not needed.

It would be nice to have a testcase to compare reference tsc versus MSR.