KVM: x86: workaround SuSE's 2.6.16 pvclock vs masterclock issue

SuSE's 2.6.16 kernel fails to boot if the delta between tsc_timestamp and rdtsc is larger than a given threshold: * If we get more than the below threshold into the future, we rerequest * the real time from the host again which has only little offset then * that we need to adjust using the TSC. * * For now that threshold is 1/5th of a jiffie. That should be good * enough accuracy for completely broken systems, but also give us swing * to not call out to the host all the time. */ #define PVCLOCK_DELTA_MAX ((1000000000ULL / HZ) / 5) Disable masterclock support (which increases said delta) in case the boot vcpu does not use MSR_KVM_SYSTEM_TIME_NEW. Upstreams kernels which support pvclock vsyscalls (and therefore make use of PVCLOCK_STABLE_BIT) use MSR_KVM_SYSTEM_TIME_NEW. Signed-off-by: Marcelo Tosatti <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
strager · Jan 20, 2015 · 54750f2 · 54750f2
1 parent 69b0049
commit 54750f2
Show file tree

Hide file tree

Showing 2 changed files with 16 additions and 1 deletion.
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
@@ -627,6 +627,8 @@ struct kvm_arch {
 	#ifdef CONFIG_KVM_MMU_AUDIT
 	int audit_point;
 	#endif
+
+	bool boot_vcpu_runs_old_kvmclock;
 };
 
 struct kvm_vm_stat {

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
@@ -1542,7 +1542,8 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm)
 					&ka->master_cycle_now);
 
 	ka->use_master_clock = host_tsc_clocksource && vcpus_matched
-				&& !backwards_tsc_observed;
+				&& !backwards_tsc_observed
+				&& !ka->boot_vcpu_runs_old_kvmclock;
 
 	if (ka->use_master_clock)
 		atomic_set(&kvm_guest_has_master_clock, 1);
@@ -2174,8 +2175,20 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_KVM_SYSTEM_TIME_NEW:
 	case MSR_KVM_SYSTEM_TIME: {
 		u64 gpa_offset;
+		struct kvm_arch *ka = &vcpu->kvm->arch;
+
 		kvmclock_reset(vcpu);
 
+		if (vcpu->vcpu_id == 0 && !msr_info->host_initiated) {
+			bool tmp = (msr == MSR_KVM_SYSTEM_TIME);
+
+			if (ka->boot_vcpu_runs_old_kvmclock != tmp)
+				set_bit(KVM_REQ_MASTERCLOCK_UPDATE,
+					&vcpu->requests);
+
+			ka->boot_vcpu_runs_old_kvmclock = tmp;
+		}
+
 		vcpu->arch.time = data;
 		kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);