----- Original Message -----
From: "Marcelo Tosatti" <[email protected]>
To: "Vadim Rozenfeld" <[email protected]>
Cc: [email protected], [email protected], [email protected]
Sent: Wednesday, May 22, 2013 10:50:46 AM
Subject: Re: [RFC PATCH v2 2/2] add support for Hyper-V invariant TSC
On Sun, May 19, 2013 at 05:06:37PM +1000, Vadim Rozenfeld wrote:
> The following patch allows to activate a partition reference
> time enlightenment that is based on the host platform's support
> for an Invariant Time Stamp Counter (iTSC).
> NOTE: This code will survive migration due to lack of VM stop/resume
> handlers, when offset, scale and sequence should be
> readjusted.
>
> ---
> arch/x86/kvm/x86.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9645dab..b423fe4 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1838,7 +1838,6 @@ static int set_msr_hyperv_pw(struct kvm_vcpu *vcpu, u32
> msr, u64 data)
> 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;
> @@ -1848,6 +1847,11 @@ static int set_msr_hyperv_pw(struct kvm_vcpu *vcpu,
> u32 msr, u64 data)
> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT);
> if (kvm_is_error_hva(addr))
> return 1;
> + tsc_ref.TscSequence =
> + boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ? 1 : 0;
1) You want NONSTOP_TSC (see 40fb1715 commit) which matches INVARIANT TSC.
[VR]
Thank you for reviewing. Will fix it.
2) TscSequence should increase?
"This field serves as a sequence number that is incremented whenever..."
[VR]
Yes, on every VM resume, including migration. After migration we also need
to recalculate scale and adjust offset.
3) 0xFFFFFFFF is the value for invalid source of reference time?
[VR] Yes, on boot-up. In this case guest will go with PMTimer (not sure about
HPET
but I can check). But if we set sequence to 0xFFFFFFFF after migration - it's
probably will not work.
> + tsc_ref.TscScale =
> + ((10000LL << 32) / vcpu->arch.virtual_tsc_khz)
> << 32;
> + tsc_ref.TscOffset = 0;
> if (__copy_to_user((void __user *)addr, &tsc_ref,
> sizeof(tsc_ref)))
> return 1;
> mark_page_dirty(kvm, gfn);
> --
> 1.8.1.2
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