On Fri, 2022-02-25 at 01:39 +0000, Sean Christopherson wrote:
> @@ -11160,7 +11162,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
> kvm_vcpu_mtrr_init(vcpu);
> vcpu_load(vcpu);
> - kvm_set_tsc_khz(vcpu, max_tsc_khz);
> + kvm_set_tsc_khz(vcpu, max_tsc_khz ? : tsc_khz);
> kvm_vcpu_reset(vcpu, false);
> kvm_init_mmu(vcpu);
> vcpu_put(vcpu);
>
Hm, now if you hit that race you end up potentially giving *different*
frequencies to different vCPUs in a single guest, depending on when
they were created.
How about this... (and as noted, I think I want to add an explicit KVM
ioctl to set kvm->arch.default_tsc_khz for subsequently created vCPUs).
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a3385db39d3e..e4696a578f41 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1119,6 +1119,8 @@ struct kvm_arch {
u64 cur_tsc_generation;
int nr_vcpus_matched_tsc;
+ u32 default_tsc_khz;
+
seqcount_raw_spinlock_t pvclock_sc;
bool use_master_clock;
u64 master_kernel_ns;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 83accd3e7502..686891966c15 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2601,6 +2601,7 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data)
* kvm_clock stable after CPU hotplug
*/
synchronizing = true;
+ data = kvm->arch.last_tsc_write;
} else {
u64 tsc_exp = kvm->arch.last_tsc_write +
nsec_to_cycles(vcpu, elapsed);
@@ -8728,22 +8729,22 @@ static int kvmclock_cpu_online(unsigned int cpu)
static void kvm_timer_init(void)
{
- max_tsc_khz = tsc_khz;
-
if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
-#ifdef CONFIG_CPU_FREQ
- struct cpufreq_policy *policy;
- int cpu;
-
- cpu = get_cpu();
- policy = cpufreq_cpu_get(cpu);
- if (policy) {
- if (policy->cpuinfo.max_freq)
- max_tsc_khz = policy->cpuinfo.max_freq;
- cpufreq_cpu_put(policy);
+ max_tsc_khz = tsc_khz;
+
+ if (IS_ENABLED(CONFIG_CPU_FREQ)) {
+ struct cpufreq_policy *policy;
+ int cpu;
+
+ cpu = get_cpu();
+ policy = cpufreq_cpu_get(cpu);
+ if (policy) {
+ if (policy->cpuinfo.max_freq)
+ max_tsc_khz = policy->cpuinfo.max_freq;
+ cpufreq_cpu_put(policy);
+ }
+ put_cpu();
}
- put_cpu();
-#endif
cpufreq_register_notifier(&kvmclock_cpufreq_notifier_block,
CPUFREQ_TRANSITION_NOTIFIER);
}
@@ -11165,7 +11166,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
kvm_xen_init_vcpu(vcpu);
kvm_vcpu_mtrr_init(vcpu);
vcpu_load(vcpu);
- kvm_set_tsc_khz(vcpu, max_tsc_khz);
+ kvm_set_tsc_khz(vcpu, vcpu->kvm->arch.default_tsc_khz);
kvm_vcpu_reset(vcpu, false);
kvm_init_mmu(vcpu);
vcpu_put(vcpu);
@@ -11614,6 +11615,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
pvclock_update_vm_gtod_copy(kvm);
raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
+ kvm->arch.default_tsc_khz = max_tsc_khz ? : tsc_khz;
kvm->arch.guest_can_read_msr_platform_info = true;
#if IS_ENABLED(CONFIG_HYPERV)
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