| Message ID | 1301042691-22929-4-git-send-email-joerg.roedel@amd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 2011-03-25 09:44, Joerg Roedel wrote: > The calculation of the tsc_delta value to ensure a > forward-going tsc for the guest is a function of the > host-tsc. This works as long as the guests tsc_khz is equal > to the hosts tsc_khz. With tsc-scaling hardware support this > is not longer true and the tsc_delta needs to be calculated > using guest_tsc values. > > Signed-off-by: Joerg Roedel <joerg.roedel@amd.com> > --- > arch/x86/kvm/x86.c | 9 +++++++-- > 1 files changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 1e7af86..47dd6ed 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2126,8 +2126,13 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) > kvm_x86_ops->vcpu_load(vcpu, cpu); > if (unlikely(vcpu->cpu != cpu) || check_tsc_unstable()) { > /* Make sure TSC doesn't go backwards */ > - s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 : > - native_read_tsc() - vcpu->arch.last_host_tsc; > + s64 tsc_delta; > + u64 tsc; > + > + kvm_get_msr(vcpu, MSR_IA32_TSC, &tsc); > + tsc_delta = !vcpu->arch.last_guest_tsc ? 0 : > + tsc - vcpu->arch.last_guest_tsc; > + > if (tsc_delta < 0) > mark_tsc_unstable("KVM discovered backwards TSC"); > if (check_tsc_unstable()) { This patch appears to cause troubles to Linux guests on TSC clocksource and APIC highres timer. The first boot after qemu start is always fine, but after a reboot the guest timer appears to fire incorrectly or even not at all. Was this patch tested with a guest reboot scenario as well? Does it account for the TSC being reset to 0 on reboot? I'm using a 2.6.38 host + kvm-kmod, but I don't see that this could be the reason. Going back one kernel commit while keeping kvm-kmod unchanged resolves the issue. Jan
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1e7af86..47dd6ed 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2126,8 +2126,13 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) kvm_x86_ops->vcpu_load(vcpu, cpu); if (unlikely(vcpu->cpu != cpu) || check_tsc_unstable()) { /* Make sure TSC doesn't go backwards */ - s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 : - native_read_tsc() - vcpu->arch.last_host_tsc; + s64 tsc_delta; + u64 tsc; + + kvm_get_msr(vcpu, MSR_IA32_TSC, &tsc); + tsc_delta = !vcpu->arch.last_guest_tsc ? 0 : + tsc - vcpu->arch.last_guest_tsc; + if (tsc_delta < 0) mark_tsc_unstable("KVM discovered backwards TSC"); if (check_tsc_unstable()) {