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

[Peter Lieven <pl@dlhnet.de>]

Am 02.01.2014 14:57, schrieb Marcelo Tosatti:
> On Thu, Jan 02, 2014 at 02:15:48PM +0100, Peter Lieven wrote:
>> Am 11.12.2013 19:53, schrieb Marcelo Tosatti:
>>> 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.
>>
>> KVM_GET_CLOCK / KVM_SET_CLOCK do the irq disable/enable pairs. What is right?
>>
>> Peter
> 
> 
>                 local_irq_disable();
>                 now_ns = get_kernel_ns();
>                 delta = user_ns.clock - now_ns;
>                 local_irq_enable();
> 
> Not using irq disable/enable pairs. The subtraction is not dependant on
> any particular time.
> 
>                 local_irq_disable();
>                 now_ns = get_kernel_ns();
>                 local_irq_enable();
>                 delta = user_ns.clock - now_ns;
> 
> Any interrupt that would affect the value of get_kernel_ns(), would
> have a similar effect before the interrupts are disabled. So the 
> disable/enable pair achieves nothing in practice. It was copied from
> kvm_guest_time_update.
> 
> 

Thanks for clarifying. What about get_kernel_ns() can't this be interrupted?

Peter