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

[Paolo Bonzini <pbonzini@redhat.com>]

Il 10/12/2013 12:23, Vadim Rozenfeld ha scritto:
> > > +		if (kvm->arch.hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE) {
> > > +			HV_REFERENCE_TSC_PAGE* tsc_ref;
> > > +			u64 curr_time;
> > > +			tsc_ref = (HV_REFERENCE_TSC_PAGE*)gfn_to_hva(kvm, 
> > > +				kvm->arch.hv_tsc_page >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT);
> > > +			tsc_ref->tsc_sequence =
> > > +				boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ? tsc_ref->tsc_sequence + 1 : 0;
> > > +			tsc_ref->tsc_scale = ((10000LL << 32) / __get_cpu_var(cpu_tsc_khz)) << 32;
> > 
> > Why shouldn't this be vcpu->arch.virtual_tsc_khz?
> 
> Yeah, I was thinking about that, but we need a vcpu instance for this.

You can perhaps store the value from vcpu->arch.virtual_tsc_khz to 
kvm->arch when the MSR is first written?

> Do you mean between HV_X64_MSR_REFERENCE_TSC which happens during
> partition creation time and KVM_SET_CLOCK which happens during resume 
> after partition pause? If so - there are several differences, where
> the offset calculation probably is the most important one.

The offset and frequence are the only differences.

+			curr_time = (((tsc_ref->tsc_scale >> 32) * native_read_tsc()) >> 32) + 
+				tsc_ref->tsc_offset;
+			tsc_ref->tsc_offset = kvm->arch.hv_ref_time - curr_time;

Why do you need kvm->arch.hv_ref_time at all?  Can you just use
"get_kernel_ns() + kvm->arch.kvmclock_offset - kvm->arch.hv_ref_count"?
Then the same code can set tsc_ref->tsc_offset in both cases.

In fact, it's not clear to me what hv_ref_time is for, and how it
is different from 

By the way, a small nit:

> 
> +		tsc_ref.tsc_sequence =
> +			boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ? 1 : 0;
> +		tsc_ref.tsc_scale =
> +			((10000LL << 32) / vcpu->arch.virtual_tsc_khz) << 32;
> +		tsc_ref.tsc_offset = 0;
>  		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;
> +		kvm->arch.hv_ref_count = 0;
>  		break;

This setting of kvm->arch.hv_ref_count belongs in the previous patch.

Paolo