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

[Paolo Bonzini <pbonzini@redhat.com>]

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?

> +			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.

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

Paolo