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

[Vadim Rozenfeld <vrozenfe@redhat.com>]

On Mon, 2013-12-09 at 15:32 +0100, Paolo Bonzini wrote:
> Il 08/12/2013 12:33, Vadim Rozenfeld ha scritto:
> > +		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;
> >  	}
> >  	default:
> > @@ -3879,6 +3884,19 @@ long kvm_arch_vm_ioctl(struct file *filp,
> >  		local_irq_enable();
> >  		kvm->arch.kvmclock_offset = delta;
> >  		kvm_gen_update_masterclock(kvm);
> > +
> > +		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.

> 
> > +			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;
> > +		}
> 
> The difference in setting tsc_ref->tsc_scale is the only important
> change between the two occurrences.  If you can avoid that difference
> and you move this to a separate function, you can reuse that new
> function in set_msr_hyperv_pw as well.

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.

Vadim.

> 
> Also, kvm_set_tsc_khz should recompute the reference page's values as
> well, so you'd have three uses.
> 
> Paolo