diff options
| -rw-r--r-- | arch/x86/include/asm/kvm_host.h | 3 | ||||
| -rw-r--r-- | arch/x86/kvm/x86.c | 31 |
2 files changed, 33 insertions, 1 deletions
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index a215153f1ff6..57b4394491ec 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -396,6 +396,9 @@ struct kvm_arch { unsigned long irq_sources_bitmap; s64 kvmclock_offset; spinlock_t tsc_write_lock; + u64 last_tsc_nsec; + u64 last_tsc_offset; + u64 last_tsc_write; struct kvm_xen_hvm_config xen_hvm_config; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 886132b6ef14..e7da14c317e6 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -898,11 +898,40 @@ static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz); void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data) { struct kvm *kvm = vcpu->kvm; - u64 offset; + u64 offset, ns, elapsed; unsigned long flags; + struct timespec ts; spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags); offset = data - native_read_tsc(); + ktime_get_ts(&ts); + monotonic_to_bootbased(&ts); + ns = timespec_to_ns(&ts); + elapsed = ns - kvm->arch.last_tsc_nsec; + + /* + * Special case: identical write to TSC within 5 seconds of + * another CPU is interpreted as an attempt to synchronize + * (the 5 seconds is to accomodate host load / swapping). + * + * In that case, for a reliable TSC, we can match TSC offsets, + * or make a best guest using kernel_ns value. + */ + if (data == kvm->arch.last_tsc_write && elapsed < 5ULL * NSEC_PER_SEC) { + if (!check_tsc_unstable()) { + offset = kvm->arch.last_tsc_offset; + pr_debug("kvm: matched tsc offset for %llu\n", data); + } else { + u64 tsc_delta = elapsed * __get_cpu_var(cpu_tsc_khz); + tsc_delta = tsc_delta / USEC_PER_SEC; + offset += tsc_delta; + pr_debug("kvm: adjusted tsc offset by %llu\n", tsc_delta); + } + ns = kvm->arch.last_tsc_nsec; + } + kvm->arch.last_tsc_nsec = ns; + kvm->arch.last_tsc_write = data; + kvm->arch.last_tsc_offset = offset; kvm_x86_ops->write_tsc_offset(vcpu, offset); spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags); |