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Revert "x86/kvm: On KVM re-enable (e.g. after suspend), update clocks"

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This reverts commit 677a73a9aa. This patch was not meant to be merged and
has issues. Revert it.

Requested-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Thomas Gleixner 2015-12-23 12:35:21 +01:00
parent f74acf0e43
commit b92c453d52
1 changed files with 72 additions and 3 deletions
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75
arch/x86/kvm/x86.c
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@ -123,6 +123,8 @@ module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR);
unsigned int __read_mostly lapic_timer_advance_ns = 0;
module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR);
static bool __read_mostly backwards_tsc_observed = false;
#define KVM_NR_SHARED_MSRS 16
struct kvm_shared_msrs_global {
@ -1669,6 +1671,7 @@ 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
&& !ka->boot_vcpu_runs_old_kvmclock;
if (ka->use_master_clock)
@ -7363,22 +7366,88 @@ int kvm_arch_hardware_enable(void)
struct kvm_vcpu *vcpu;
int i;
int ret;
u64 local_tsc;
u64 max_tsc = 0;
bool stable, backwards_tsc = false;
kvm_shared_msr_cpu_online();
ret = kvm_x86_ops->hardware_enable();
if (ret != 0)
return ret;
local_tsc = rdtsc();
stable = !check_tsc_unstable();
list_for_each_entry(kvm, &vm_list, vm_list) {
kvm_for_each_vcpu(i, vcpu, kvm) {
if (vcpu->cpu == smp_processor_id()) {
if (!stable && vcpu->cpu == smp_processor_id())
kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE,
vcpu);
if (stable && vcpu->arch.last_host_tsc > local_tsc) {
backwards_tsc = true;
if (vcpu->arch.last_host_tsc > max_tsc)
max_tsc = vcpu->arch.last_host_tsc;
}
}
}
/*
* Sometimes, even reliable TSCs go backwards. This happens on
* platforms that reset TSC during suspend or hibernate actions, but
* maintain synchronization. We must compensate. Fortunately, we can
* detect that condition here, which happens early in CPU bringup,
* before any KVM threads can be running. Unfortunately, we can't
* bring the TSCs fully up to date with real time, as we aren't yet far
* enough into CPU bringup that we know how much real time has actually
* elapsed; our helper function, get_kernel_ns() will be using boot
* variables that haven't been updated yet.
*
* So we simply find the maximum observed TSC above, then record the
* adjustment to TSC in each VCPU. When the VCPU later gets loaded,
* the adjustment will be applied. Note that we accumulate
* adjustments, in case multiple suspend cycles happen before some VCPU
* gets a chance to run again. In the event that no KVM threads get a
* chance to run, we will miss the entire elapsed period, as we'll have
* reset last_host_tsc, so VCPUs will not have the TSC adjusted and may
* loose cycle time. This isn't too big a deal, since the loss will be
* uniform across all VCPUs (not to mention the scenario is extremely
* unlikely). It is possible that a second hibernate recovery happens
* much faster than a first, causing the observed TSC here to be
* smaller; this would require additional padding adjustment, which is
* why we set last_host_tsc to the local tsc observed here.
*
* N.B. - this code below runs only on platforms with reliable TSC,
* as that is the only way backwards_tsc is set above. Also note
* that this runs for ALL vcpus, which is not a bug; all VCPUs should
* have the same delta_cyc adjustment applied if backwards_tsc
* is detected. Note further, this adjustment is only done once,
* as we reset last_host_tsc on all VCPUs to stop this from being
* called multiple times (one for each physical CPU bringup).
*
* Platforms with unreliable TSCs don't have to deal with this, they
* will be compensated by the logic in vcpu_load, which sets the TSC to
* catchup mode. This will catchup all VCPUs to real time, but cannot
* guarantee that they stay in perfect synchronization.
*/
if (backwards_tsc) {
u64 delta_cyc = max_tsc - local_tsc;
backwards_tsc_observed = true;
list_for_each_entry(kvm, &vm_list, vm_list) {
kvm_for_each_vcpu(i, vcpu, kvm) {
vcpu->arch.tsc_offset_adjustment += delta_cyc;
vcpu->arch.last_host_tsc = local_tsc;
kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);
}
/*
* We have to disable TSC offset matching.. if you were
* booting a VM while issuing an S4 host suspend....
* you may have some problem. Solving this issue is
* left as an exercise to the reader.
*/
kvm->arch.last_tsc_nsec = 0;
kvm->arch.last_tsc_write = 0;
}
}
return 0;
}