Re: [RFC PATCH v5] add support for Hyper-V reference time counter

[Vadim Rozenfeld <vrozenfe@redhat.com>]

On Fri, 2014-01-17 at 14:25 +0100, Paolo Bonzini wrote:
> Il 17/01/2014 14:18, Marcelo Tosatti ha scritto:
> > On Fri, Jan 17, 2014 at 10:06:00PM +1100, Vadim Rozenfeld wrote:
> >> On Thu, 2014-01-16 at 20:23 -0200, Marcelo Tosatti wrote:
> >>> On Thu, Jan 16, 2014 at 08:18:37PM +1100, Vadim Rozenfeld wrote:
> >>>> Signed-off: Peter Lieven <pl@kamp.de>
> >>>> Signed-off: Gleb Natapov
> >>>> Signed-off: Vadim Rozenfeld <vrozenfe@redhat.com>
> >>>>  
> >>>> After some consideration I decided to submit only Hyper-V reference
> >>>> counters support this time. I will submit iTSC support as a separate
> >>>> patch as soon as it is ready. 
> >>>>
> >>>> 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@amp.de>
> >>>> 3. move check for TSC page enable from second patch
> >>>>     to this one.
> >>>>
> >>>> v3 -> v4
> >>>>     Get rid of ref counter offset.
> >>>>
> >>>> v4 -> v5
> >>>>     replace __copy_to_user with kvm_write_guest
> >>>>     when updateing iTSC page.
> >>>>
> >>>> ---
> >>>>  arch/x86/include/asm/kvm_host.h    |  1 +
> >>>>  arch/x86/include/uapi/asm/hyperv.h | 13 +++++++++++++
> >>>>  arch/x86/kvm/x86.c                 | 28 +++++++++++++++++++++++++++-
> >>>>  include/uapi/linux/kvm.h           |  1 +
> >>>>  4 files changed, 42 insertions(+), 1 deletion(-)
> >>>>
> >>>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> >>>> index ae5d783..33fef07 100644
> >>>> --- a/arch/x86/include/asm/kvm_host.h
> >>>> +++ b/arch/x86/include/asm/kvm_host.h
> >>>> @@ -605,6 +605,7 @@ struct kvm_arch {
> >>>>  	/* fields used by HYPER-V emulation */
> >>>>  	u64 hv_guest_os_id;
> >>>>  	u64 hv_hypercall;
> >>>> +	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 5d004da..8e685b8 100644
> >>>> --- a/arch/x86/kvm/x86.c
> >>>> +++ b/arch/x86/kvm/x86.c
> >>>> @@ -836,11 +836,12 @@ EXPORT_SYMBOL_GPL(kvm_rdpmc);
> >>>>   * kvm-specific. Those are put in the beginning of the list.
> >>>>   */
> >>>>  
> >>>> -#define KVM_SAVE_MSRS_BEGIN	10
> >>>> +#define KVM_SAVE_MSRS_BEGIN	12
> >>>>  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_TIME_REF_COUNT, HV_X64_MSR_REFERENCE_TSC,
> >>>>  	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 +1827,8 @@ 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;
> >>>>  	}
> >>>> @@ -1867,6 +1870,20 @@ static int set_msr_hyperv_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data)
> >>>>  		kvm->arch.hv_hypercall = data;
> >>>>  		break;
> >>>>  	}
> >>>> +	case HV_X64_MSR_REFERENCE_TSC: {
> >>>> +		u64 gfn;
> >>>> +		HV_REFERENCE_TSC_PAGE tsc_ref;
> >>>> +		memset(&tsc_ref, 0, sizeof(tsc_ref));
> >>>> +		kvm->arch.hv_tsc_page = data;
> >>>
> >>> Comment 1)
> >>>
> >>> Is there a reason (that is compliance with spec) to maintain
> >>> value, for HV_X64_MSR_REFERENCE_TSC wrmsr operation, in case
> >>> HV_X64_MSR_TSC_REFERENCE_ENABLE is not set?
> >>  
> >> Windows seems to be retrieving HV_X64_MSR_REFERENCE_TSC value only once
> >> on boot-up, checks HV_X64_MSR_TSC_REFERENCE_ENABLE bit allocate one page
> >> and maps it into the system space, and writes the page address to
> >> HV_X64_MSR_REFERENCE_TSC MSR if this bit was not set. Windows keeps the
> >> TSC page address value in HvlReferenceTscPage variable and uses it
> >> every time when needs to read the TSC page content.
> > 
> > Ok then it has to be saved/restored irrespective of the value of
> > HV_X64_MSR_TSC_REFERENCE_ENABLE.
> > 
> >>> If not, should only assign to kvm->arch.hv_tsc_page after proper checks.
> >>>
> >>>> +		if (!(data & HV_X64_MSR_TSC_REFERENCE_ENABLE))
> >>>> +			break;
> >>>> +		gfn = data >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;
> >>>> +		if (kvm_write_guest(kvm, data,
> >>>> +			&tsc_ref, sizeof(tsc_ref)))
> >>>> +			return 1;
> >>>> +		mark_page_dirty(kvm, gfn);
> >>>> +		break;
> >>>> +	}
> >>>>  	default:
> >>>>  		vcpu_unimpl(vcpu, "HYPER-V unimplemented wrmsr: 0x%x "
> >>>>  			    "data 0x%llx\n", msr, data);
> >>>> @@ -2291,6 +2308,14 @@ 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: {
> >>>> +		data =
> >>>> +		     div_u64(get_kernel_ns() + kvm->arch.kvmclock_offset, 100);
> >>>
> >>> Comment 2)
> >>>
> >>> Is there any specification related to the initial value of the clock
> >>> after it is enabled ?
> >>
> >> The MS documentation says the following:
> >> "A partition's reference time counter is initialized to zero when the
> >> partition is created. The reference time counter for all partitions
> >> count at the same rate. However, at any time, the absolute value of each
> >> reference time counter will typically differ because partitions will
> >> have different creation times."
> >>
> >> http://msdn.microsoft.com/en-us/library/windows/hardware/ff542637%
> >> 28v=vs.85%29.aspx
> >>
> >> However, Windows doesn't seem to be worried about the initial value.
> >> HvlGetReferenceTime only reads  HV_X64_MSR_TIME_REF_COUNT MSR and
> >> returns the obtained value.
> > 
> > Right. It might be better to initialize kvmclock_offset to zero 
> > in case of VM creation (QEMU's PUT_FULL state), in case Hyper-V timers
> > enabled, with reference to MS docs on top.
> > 
> > Otherwise might end up hitting Windows code timers bugs.
> > 
> > But its a potential improvement, patch looks good.
> > 
> >>>> +	}
> >>>> +	case HV_X64_MSR_REFERENCE_TSC:
> >>>> +		data = kvm->arch.hv_tsc_page;
> >>>> +		break;
> >>>>  	default:
> >>>>  		vcpu_unimpl(vcpu, "Hyper-V unhandled rdmsr: 0x%x\n", msr);
> >>>>  		return 1;
> >>>> @@ -2604,6 +2629,7 @@ int kvm_dev_ioctl_check_extension(long ext)
> >>>>  #ifdef CONFIG_KVM_DEVICE_ASSIGNMENT
> >>>>  	case KVM_CAP_ASSIGN_DEV_IRQ:
> >>>>  	case KVM_CAP_PCI_2_3:
> >>>> +	case KVM_CAP_HYPERV_TIME:
> >>>>  #endif
> >>>>  		r = 1;
> >>>>  		break;
> >>>> 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
> >>>>
> >>>
> >>> Comment 3) 
> >>>
> >>> Missing qemu HV_X64_MSR_REFERENCE_TSC save/restore.
> >> I have this code ready. I'm going to send it to qemu 
> >> list as soon as KVM patch will be accepted.
> > 
> > Looks good to me.
> > 
> 
> Applied to kvm/queue, thanks!
Great.
Thank you guys for your help.
Vadim.
> 
> Paolo