Re: [RFC PATCH v3 1/2] add support for Hyper-V reference time counter

[Marcelo Tosatti <mtosatti@redhat.com>]

On Sun, Dec 08, 2013 at 10:33:38PM +1100, 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 | 13 +++++++++++++
>  arch/x86/kvm/x86.c                 | 39 +++++++++++++++++++++++++++++++++++++-
>  include/uapi/linux/kvm.h           |  1 +
>  4 files changed, 54 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index ae5d783..2fd0753 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -605,6 +605,8 @@ 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 b8f1c01..462efe7 100644
> --- a/arch/x86/include/uapi/asm/hyperv.h
> +++ b/arch/x86/include/uapi/asm/hyperv.h
> @@ -28,6 +28,9 @@
>  /* Partition Reference Counter (HV_X64_MSR_TIME_REF_COUNT) available*/
>  #define HV_X64_MSR_TIME_REF_COUNT_AVAILABLE	(1 << 1)
>  
> +/* A partition's reference time stamp counter (TSC) page */
> +#define HV_X64_MSR_REFERENCE_TSC		0x40000021
> +
>  /*
>   * 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
> @@ -198,6 +201,9 @@
>  #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
> @@ -210,4 +216,11 @@
>  #define HV_STATUS_INVALID_ALIGNMENT		4
>  #define HV_STATUS_INSUFFICIENT_BUFFERS		19
>  
> +typedef struct _HV_REFERENCE_TSC_PAGE {
> +	__u32 tsc_sequence;
> +	__u32 res1;
> +	__u64 tsc_scale;
> +	__s64 tsc_offset;
> +} HV_REFERENCE_TSC_PAGE, *PHV_REFERENCE_TSC_PAGE;
> +
>  #endif
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 21ef1ba..5e4e495a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -840,7 +840,7 @@ 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,
> -	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,
> @@ -1826,6 +1826,8 @@ 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;
>  	}
> @@ -1865,6 +1867,29 @@ 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() + kvm->arch.kvmclock_offset;
> +		local_irq_enable();

Where does the docs say that HV_X64_MSR_HYPERCALL is the where the clock
starts counting?

No need to store kvmclock_offset in hv_ref_count? (moreover
the name is weird, better name would be "hv_ref_start_time".

> +		break;
> +	}
> +	case HV_X64_MSR_REFERENCE_TSC: {
> +		u64 gfn;
> +		unsigned long addr;
> +		HV_REFERENCE_TSC_PAGE tsc_ref;
> +		tsc_ref.tsc_sequence = 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:
> @@ -2291,6 +2316,17 @@ 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();

No need for irq disable/enable pairs.

> +		break;
> +	}
> +	case HV_X64_MSR_REFERENCE_TSC:
> +		data = kvm->arch.hv_tsc_page;
> +		break;

Does it return non-zero data even if not enabled?

>  	default:
>  		vcpu_unimpl(vcpu, "Hyper-V unhandled rdmsr: 0x%x\n", msr);
>  		return 1;
> @@ -2605,6 +2641,7 @@ int kvm_dev_ioctl_check_extension(long ext)
>  	case KVM_CAP_ASSIGN_DEV_IRQ:
>  	case KVM_CAP_PCI_2_3:
>  #endif
> +	case KVM_CAP_HYPERV_TIME:
>  		r = 1;
>  		break;
>  	case KVM_CAP_COALESCED_MMIO:
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 902f124..686c1ca 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -674,6 +674,7 @@ struct kvm_ppc_smmu_info {
>  #define KVM_CAP_ARM_EL1_32BIT 93
>  #define KVM_CAP_SPAPR_MULTITCE 94
>  #define KVM_CAP_EXT_EMUL_CPUID 95
> +#define KVM_CAP_HYPERV_TIME 96
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> -- 
> 1.8.1.4