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

[Gleb Natapov <gleb@redhat.com>]

On Tue, May 21, 2013 at 09:46:14PM -0300, Marcelo Tosatti wrote:
> 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.
>
get_kernel_ns has WARN_ON(preemptible()) so at least preempt_disable()
is needed, but all callers of the function disable interrupts.

> What is the reasoning behind reading this time value at msr write time?
> 
> > +	}
> > +	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.

--
			Gleb.