On Mon, Jan 13, 2014 at 11:11:40PM -0500, Vadim Rozenfeld wrote:
>
>
> ----- Original Message -----
> From: "Marcelo Tosatti" <mtosa...@redhat.com>
> To: "Vadim Rozenfeld" <vroze...@redhat.com>
> Cc: kvm@vger.kernel.org, p...@dlhnet.de, pbonz...@redhat.com
> Sent: Thursday, December 12, 2013 6:27:00 AM
> Subject: Re: [RFC PATCH v3 2/2] add support for Hyper-V partition reference
> time enlightenment
>
> On Sun, Dec 08, 2013 at 10:33:39PM +1100, 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).
> >
> > v2 -> v3
> > Handle TSC sequence, scale, and offest changing during migration.
> >
> > ---
> > arch/x86/include/asm/kvm_host.h | 1 +
> > arch/x86/kvm/x86.c | 29 +++++++++++++++++++++++++++--
> > 2 files changed, 28 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h
> > b/arch/x86/include/asm/kvm_host.h
> > index 2fd0753..81fdff0 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -607,6 +607,7 @@ struct kvm_arch {
> > u64 hv_hypercall;
> > u64 hv_ref_count;
> > u64 hv_tsc_page;
> > + u64 hv_ref_time;
> >
> > #ifdef CONFIG_KVM_MMU_AUDIT
> > int audit_point;
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 5e4e495a..cb6766a 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -1882,14 +1882,19 @@ static int set_msr_hyperv_pw(struct kvm_vcpu *vcpu,
> > u32 msr, u64 data)
> > break;
> > }
> > gfn = data >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;
> > - addr = gfn_to_hva(kvm, data >>
> > - HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT);
> > + addr = gfn_to_hva(kvm, gfn);
> > if (kvm_is_error_hva(addr))
> > return 1;
> > + 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;
> > + 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;
> > + }
> > break;
> > }
> > case KVM_GET_CLOCK: {
> > @@ -3896,6 +3914,13 @@ long kvm_arch_vm_ioctl(struct file *filp,
> > if (copy_to_user(argp, &user_ns, sizeof(user_ns)))
> > goto out;
> > r = 0;
> > + if (kvm->arch.hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE) {
> > + HV_REFERENCE_TSC_PAGE* tsc_ref;
> > + tsc_ref = (HV_REFERENCE_TSC_PAGE*)gfn_to_hva(kvm,
> > + kvm->arch.hv_tsc_page >>
> > HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT);
>
> kvm_read_guest_cached.
>
> > + kvm->arch.hv_ref_time = (((tsc_ref->tsc_scale >> 32) *
> > + native_read_tsc()) >> 32) + tsc_ref->tsc_offset;
>
> Why native_read_tsc and not ->read_l1_tsc?
>
> [VR]
> Is it possible to get pointer to the vcpu instance at this point?
See the suggestion to move this code to kvm_guest_time_update.
> Thanks,
> Vadim.
>
> It is easier to trust on the host to check reliability of the TSC: if
> it uses TSC clocksource, then the TSCs are stable. So could condition
> exposing the TSC ref page when ka->use_master_clock=1, see
> kvm_guest_time_update.
> And hook into pvclock_gtod_notify.
>
> So in addition to X86_FEATURE_CONSTANT_TSC, check
> ka->use_master_clock=1
>
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