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

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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@xxxxxxx>
Signed-off: Gleb Natapov <gleb@xxxxxxxxxx>
Signed-off: Vadim Rozenfeld <vrozenfe@xxxxxxxxxx>

v1 -> v2
1. mark TSC page dirty as suggested by
     Eric Northup <digitaleric@xxxxxxxxxx> and Gleb
2. disable local irq when calling get_kernel_ns,
     as it was done by Peter Lieven <pl@xxxxxxxxx>
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

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