Re: [RFC PATCH 1/2] Hyper-H reference counter

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On Tue, May 14, 2013 at 04:14:11PM +0200, Peter Lieven wrote:
> On 13.05.2013 13:45, Vadim Rozenfeld wrote:
> >Signed-off: Peter Lieven <pl@xxxxxxx>
> >Signed-off: Gleb Natapov <gleb@xxxxxxxxxx>
> >Signed-off: Vadim Rozenfeld <vrozenfe@xxxxxxxxxx>
> >
> >The following patch allows to activate Hyper-V
> >reference time counter
> >---
> >  arch/x86/include/asm/kvm_host.h    |  2 ++
> >  arch/x86/include/uapi/asm/hyperv.h |  3 +++
> >  arch/x86/kvm/x86.c                 | 25 ++++++++++++++++++++++++-
> >  3 files changed, 29 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..9711819 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
> >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >index 094b5d9..1a4036d 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,
> >-	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,
> >@@ -1764,6 +1764,8 @@ 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;
> >  	}
> >@@ -1803,6 +1805,21 @@ 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;
> >+		kvm->arch.hv_ref_count = get_kernel_ns();
> >+		break;
> >+	}
> >+	case HV_X64_MSR_REFERENCE_TSC: {
> >+		u64 gfn;
> >+		unsigned long addr;
> >+		u32 tsc_ref;
> >+		gfn = data >> HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_SHIFT;
> >+		addr = gfn_to_hva(kvm, gfn);
> >+		if (kvm_is_error_hva(addr))
> >+			return 1;
> >+		tsc_ref = 0;
> >+		if(__copy_to_user((void __user *)addr, &tsc_ref, sizeof(tsc_ref)))
> >+			return 1;
> >+		kvm->arch.hv_tsc_page = data;
> >  		break;
> >  	}
> >  	default:
> >@@ -2229,6 +2246,12 @@ 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.hv_ref_count,100);
> >+		break;
> 
> 
> in an earlier version of this patch I have the following:
> 
> +       case HV_X64_MSR_TIME_REF_COUNT: {
> +               u64 now_ns;
> +               local_irq_disable();
> +               now_ns = get_kernel_ns();
> +               data = div_u64(now_ns + kvm->arch.kvmclock_offset - kvm->arch.hv_ref_count,100);
> +               local_irq_enable();
> +               break;
> +       }
> 
> I do not know if this is right, but I can report that this one is working without any flaws
> since approx. 1.5 years.
> 
get_kernel_ns() should be called at least with preemption disabled and
all other callers disable irq around it too, also without
kvmclock_offset the counter will be incorrect after migration. Marcelo,
is kvmclock_offset guaranties migration correctness or more is required?

--
			Gleb.
--
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