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KVM: x86: use raw clock values consistently

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Commit 53fafdbb8b ("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: 53fafdbb8b ("KVM: x86: switch KVMCLOCK base to monotonic raw clock")
Cc: stable@vger.kernel.org
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2020-01-22 14:36:09 +01:00
parent 917f9475c0
commit 8171cd6880
1 changed files with 23 additions and 15 deletions
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38
arch/x86/kvm/x86.c
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@ -1655,6 +1655,18 @@ static void update_pvclock_gtod(struct timekeeper *tk)
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)
@ -1668,7 +1680,7 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
int version;
int r;
struct pvclock_wall_clock wc;
struct timespec64 boot;
u64 wall_nsec;
if (!wall_clock)
return;
@ -1688,17 +1700,12 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
/*
* 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));
@ -1946,7 +1953,7 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
offset = kvm_compute_tsc_offset(vcpu, data);
ns = ktime_get_boottime_ns();
ns = get_kvmclock_base_ns();
elapsed = ns - kvm->arch.last_tsc_nsec;
if (vcpu->arch.virtual_tsc_khz) {
@ -2284,7 +2291,7 @@ 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_boottime_ns() + ka->kvmclock_offset;
return get_kvmclock_base_ns() + ka->kvmclock_offset;
}
hv_clock.tsc_timestamp = ka->master_cycle_now;
@ -2300,7 +2307,7 @@ u64 get_kvmclock_ns(struct kvm *kvm)
&hv_clock.tsc_to_system_mul);
ret = __pvclock_read_cycles(&hv_clock, rdtsc());
} else
ret = ktime_get_boottime_ns() + ka->kvmclock_offset;
ret = get_kvmclock_base_ns() + ka->kvmclock_offset;
put_cpu();
@ -2399,7 +2406,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
}
if (!use_master_clock) {
host_tsc = rdtsc();
kernel_ns = ktime_get_boottime_ns();
kernel_ns = get_kvmclock_base_ns();
}
tsc_timestamp = kvm_read_l1_tsc(v, host_tsc);
@ -2439,6 +2446,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
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;
@ -9677,7 +9685,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
mutex_init(&kvm->arch.apic_map_lock);
spin_lock_init(&kvm->arch.pvclock_gtod_sync_lock);
kvm->arch.kvmclock_offset = -ktime_get_boottime_ns();
kvm->arch.kvmclock_offset = -get_kvmclock_base_ns();
pvclock_update_vm_gtod_copy(kvm);
kvm->arch.guest_can_read_msr_platform_info = true;