BZ: 1768622 Brew: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=28587593 commit 8171cd68806bd2fc28ef688e32fb2a3b3deb04e5 Commit 53fafdbb8b21f ("KVM: x86: switch KVMCLOCK base to monotonic raw clock") changed kvmclock to use tkr_raw instead of tkr_mono. However, the default kvmclock_offset for the VM was still based on the monotonic clock and, if the raw clock drifted enough from the monotonic clock, this could cause a negative system_time to be written to the guest's struct pvclock. RHEL5 does not like it and (if it boots fast enough to observe a negative time value) it hangs. There is another thing to be careful about: getboottime64 returns the host boot time with tkr_mono frequency, and subtracting the tkr_raw-based kvmclock value will cause the wallclock to be off if tkr_raw drifts from tkr_mono. To avoid this, compute the wallclock delta from the current time instead of being clever and using getboottime64. Fixes: 53fafdbb8b21f ("KVM: x86: switch KVMCLOCK base to monotonic raw clock") Cc: stable@xxxxxxxxxxxxxxx Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Index: kernel-rhel/arch/x86/kvm/x86.c =================================================================== --- kernel-rhel.orig/arch/x86/kvm/x86.c +++ kernel-rhel/arch/x86/kvm/x86.c @@ -1595,6 +1595,18 @@ static void update_pvclock_gtod(struct t write_seqcount_end(&vdata->seq); } + +static s64 get_kvmclock_base_ns(void) +{ + /* Count up from boot time, but with the frequency of the raw clock. */ + return ktime_to_ns(ktime_add(ktime_get_raw(), pvclock_gtod_data.offs_boot)); +} +#else +static s64 get_kvmclock_base_ns(void) +{ + /* Master clock not used, so we can just use CLOCK_BOOTTIME. */ + return ktime_get_boottime_ns(); +} #endif void kvm_set_pending_timer(struct kvm_vcpu *vcpu) @@ -1608,7 +1620,7 @@ static void kvm_write_wall_clock(struct int version; int r; struct pvclock_wall_clock wc; - struct timespec64 boot; + u64 wall_nsec; if (!wall_clock) return; @@ -1628,17 +1640,12 @@ static void kvm_write_wall_clock(struct /* * The guest calculates current wall clock time by adding * system time (updated by kvm_guest_time_update below) to the - * wall clock specified here. guest system time equals host - * system time for us, thus we must fill in host boot time here. + * wall clock specified here. We do the reverse here. */ - getboottime64(&boot); + wall_nsec = ktime_get_real_ns() - get_kvmclock_ns(kvm); - if (kvm->arch.kvmclock_offset) { - struct timespec64 ts = ns_to_timespec64(kvm->arch.kvmclock_offset); - boot = timespec64_sub(boot, ts); - } - wc.sec = (u32)boot.tv_sec; /* overflow in 2106 guest time */ - wc.nsec = boot.tv_nsec; + wc.nsec = do_div(wall_nsec, 1000000000); + wc.sec = (u32)wall_nsec; /* overflow in 2106 guest time */ wc.version = version; kvm_write_guest(kvm, wall_clock, &wc, sizeof(wc)); @@ -1886,7 +1893,7 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags); offset = kvm_compute_tsc_offset(vcpu, data); - ns = ktime_get_boot_ns(); + ns = get_kvmclock_base_ns(); elapsed = ns - kvm->arch.last_tsc_nsec; if (vcpu->arch.virtual_tsc_khz) { @@ -2224,7 +2231,7 @@ u64 get_kvmclock_ns(struct kvm *kvm) spin_lock(&ka->pvclock_gtod_sync_lock); if (!ka->use_master_clock) { spin_unlock(&ka->pvclock_gtod_sync_lock); - return ktime_get_boot_ns() + ka->kvmclock_offset; + return get_kvmclock_base_ns() + ka->kvmclock_offset; } hv_clock.tsc_timestamp = ka->master_cycle_now; @@ -2240,7 +2247,7 @@ u64 get_kvmclock_ns(struct kvm *kvm) &hv_clock.tsc_to_system_mul); ret = __pvclock_read_cycles(&hv_clock, rdtsc()); } else - ret = ktime_get_boot_ns() + ka->kvmclock_offset; + ret = get_kvmclock_base_ns() + ka->kvmclock_offset; put_cpu(); @@ -2339,7 +2346,7 @@ static int kvm_guest_time_update(struct } if (!use_master_clock) { host_tsc = rdtsc(); - kernel_ns = ktime_get_boot_ns(); + kernel_ns = get_kvmclock_base_ns(); } tsc_timestamp = kvm_read_l1_tsc(v, host_tsc); @@ -2379,6 +2386,7 @@ static int kvm_guest_time_update(struct vcpu->hv_clock.tsc_timestamp = tsc_timestamp; vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset; vcpu->last_guest_tsc = tsc_timestamp; + WARN_ON(vcpu->hv_clock.system_time < 0); /* If the host uses TSC clocksource, then it is stable */ pvclock_flags = 0; @@ -9486,7 +9494,7 @@ int kvm_arch_init_vm(struct kvm *kvm, un mutex_init(&kvm->arch.apic_map_lock); spin_lock_init(&kvm->arch.pvclock_gtod_sync_lock); - kvm->arch.kvmclock_offset = -ktime_get_boot_ns(); + kvm->arch.kvmclock_offset = -get_kvmclock_base_ns(); pvclock_update_vm_gtod_copy(kvm); kvm->arch.guest_can_read_msr_platform_info = true;
