| Message ID | 20200616114741.GA298183@fuller.cnet (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] KVM: x86: allow TSC to differ by NTP correction bounds without TSC scaling | expand |
On 16/06/20 13:47, Marcelo Tosatti wrote: > v2: improve changelog (Paolo Bonzini) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 3156e25..39a6664 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1772,6 +1772,8 @@ static int set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz, bool scale) > > /* TSC scaling supported? */ > if (!kvm_has_tsc_control) { > + if (!scale) > + return 0; This cannot happen, there is an "if (!scale) right above. > if (user_tsc_khz > tsc_khz) { > vcpu->arch.tsc_catchup = 1; > vcpu->arch.tsc_always_catchup = 1; > @@ -4473,7 +4475,8 @@ long kvm_arch_vcpu_ioctl(struct file *filp, > r = -EINVAL; > user_tsc_khz = (u32)arg; > > - if (user_tsc_khz >= kvm_max_guest_tsc_khz) > + if (kvm_has_tsc_control && > + user_tsc_khz >= kvm_max_guest_tsc_khz) > goto out; > > if (user_tsc_khz == 0) > Queued this second hunk. Paolo
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 3156e25..39a6664 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1772,6 +1772,8 @@ static int set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz, bool scale) /* TSC scaling supported? */ if (!kvm_has_tsc_control) { + if (!scale) + return 0; if (user_tsc_khz > tsc_khz) { vcpu->arch.tsc_catchup = 1; vcpu->arch.tsc_always_catchup = 1; @@ -4473,7 +4475,8 @@ long kvm_arch_vcpu_ioctl(struct file *filp, r = -EINVAL; user_tsc_khz = (u32)arg; - if (user_tsc_khz >= kvm_max_guest_tsc_khz) + if (kvm_has_tsc_control && + user_tsc_khz >= kvm_max_guest_tsc_khz) goto out; if (user_tsc_khz == 0)
The Linux TSC calibration procedure is subject to small variations (its common to see +-1 kHz difference between reboots on a given CPU, for example). So migrating a guest between two hosts with identical processor can fail, in case of a small variation in calibrated TSC between them. Without TSC scaling, the current kernel interface will either return an error (if user_tsc_khz <= tsc_khz) or enable TSC catchup mode. This change enables the following TSC tolerance check to accept KVM_SET_TSC_KHZ within tsc_tolerance_ppm (which is 250ppm by default). /* * Compute the variation in TSC rate which is acceptable * within the range of tolerance and decide if the * rate being applied is within that bounds of the hardware * rate. If so, no scaling or compensation need be done. */ thresh_lo = adjust_tsc_khz(tsc_khz, -tsc_tolerance_ppm); thresh_hi = adjust_tsc_khz(tsc_khz, tsc_tolerance_ppm); if (user_tsc_khz < thresh_lo || user_tsc_khz > thresh_hi) { pr_debug("kvm: requested TSC rate %u falls outside tolerance [%u,%u]\n", user_tsc_khz, thresh_lo, thresh_hi); use_scaling = 1; } NTP daemon in the guest can correct this difference (NTP can correct upto 500ppm). Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> --- v2: improve changelog (Paolo Bonzini)