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

[Peter Lieven <pl@dlhnet.de>]

On 08.01.2014 10:40, Vadim Rozenfeld wrote:
> On Tue, 2014-01-07 at 18:52 +0100, Peter Lieven wrote:
>> Am 07.01.2014 10:36, schrieb Vadim Rozenfeld:
>>> On Thu, 2014-01-02 at 17:52 +0100, Peter Lieven wrote:
>>>> Am 11.12.2013 19:59, schrieb Marcelo Tosatti:
>>>>> On Wed, Dec 11, 2013 at 04:53:05PM -0200, Marcelo Tosatti wrote:
>>>>>> 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".
>>>>>
>>>>> Just add kvmclock_offset when reading the values (otherwise you have a
>>>>> "stale copy" of kvmclock_offset in hv_ref_count).
>>>>>
>>>>
>>>> After some experiments I think we do no need kvm->arch.hv_ref_count at all.
>>>>
>>>> I was debugging some weird clockjump issues and I think the problem is that after live migration
>>>> kvm->arch.hv_ref_count is initialized to 0. Depending on the uptime of the vServer when the
>>>> hypercall was set up this can lead to series jumps.
>>>>
>>>> So I would suggest to completely drop kvm->arch.hv_ref_count.
>>>>
>>>> And use simply this in get_msr_hyperv_pw().
>>>>
>>>>          case HV_X64_MSR_TIME_REF_COUNT: {
>>>>                  data = div_u64(get_kernel_ns() + kvm->arch.kvmclock_offset, 100);
>>>>                  break;
>>>>          }
>>>>
>>>
>>> Agreed. It should work as long as we rely on kvmclock_offset.
>>> Vadim.
>>
>> I think we can rely on kvmclock_offset. Had you had a chance to do further testing
>> during the weekend?
>
> Yes, and still testing.
>
> There is still some inconsistency in the value returned by
> QueryPerformanceCounter during migration.

With my proposal?

Peter