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KVM: X86: Make tsc_delta calculation a function of guest tsc

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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>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Joerg Roedel 2011-03-25 09:44:48 +01:00 committed by Avi Kivity
parent 1e993611d0
commit 8f6055cbaf
1 changed files with 7 additions and 2 deletions
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9
arch/x86/kvm/x86.c
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@ -2113,8 +2113,13 @@ 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()) {