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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 <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
hifive-unleashed-5.1
Marcelo Tosatti 2015-01-20 15:54:52 -02:00 committed by Paolo Bonzini
parent 69b0049a89
commit 54750f2cf0
2 changed files with 16 additions and 1 deletions
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2
arch/x86/include/asm/kvm_host.h
View File

@ -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 {

15
arch/x86/kvm/x86.c
View File

@ -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);