On Thu, Sep 16, 2021 at 06:15:36PM +0000, Oliver Upton wrote: > From: Paolo Bonzini <[email protected]> > > Protect the reference point for kvmclock with a seqcount, so that > kvmclock updates for all vCPUs can proceed in parallel. Xen runstate > updates will also run in parallel and not bounce the kvmclock cacheline. > > nr_vcpus_matched_tsc is updated outside pvclock_update_vm_gtod_copy > though, so a spinlock must be kept for that one. > > Signed-off-by: Paolo Bonzini <[email protected]> > [Oliver - drop unused locals, don't double acquire tsc_write_lock] > Signed-off-by: Oliver Upton <[email protected]> > --- > arch/x86/include/asm/kvm_host.h | 7 ++- > arch/x86/kvm/x86.c | 83 +++++++++++++++++---------------- > 2 files changed, 49 insertions(+), 41 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 9c34b5b63e39..5accfe7246ce 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1087,6 +1087,11 @@ struct kvm_arch { > > unsigned long irq_sources_bitmap; > s64 kvmclock_offset; > + > + /* > + * This also protects nr_vcpus_matched_tsc which is read from a > + * preemption-disabled region, so it must be a raw spinlock. > + */ > raw_spinlock_t tsc_write_lock; > u64 last_tsc_nsec; > u64 last_tsc_write; > @@ -1097,7 +1102,7 @@ struct kvm_arch { > u64 cur_tsc_generation; > int nr_vcpus_matched_tsc; > > - spinlock_t pvclock_gtod_sync_lock; > + seqcount_raw_spinlock_t pvclock_sc; > bool use_master_clock; > u64 master_kernel_ns; > u64 master_cycle_now; > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index cb5d5cad5124..29156c49cd11 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2533,9 +2533,7 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, > u64 data) > vcpu->arch.this_tsc_write = kvm->arch.cur_tsc_write; > > kvm_vcpu_write_tsc_offset(vcpu, offset); > - raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags); > > - spin_lock_irqsave(&kvm->arch.pvclock_gtod_sync_lock, flags); > if (!matched) { > kvm->arch.nr_vcpus_matched_tsc = 0; > } else if (!already_matched) { > @@ -2543,7 +2541,7 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, > u64 data) > } > > kvm_track_tsc_matching(vcpu); > - spin_unlock_irqrestore(&kvm->arch.pvclock_gtod_sync_lock, flags); > + raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags); > } > > static inline void adjust_tsc_offset_guest(struct kvm_vcpu *vcpu, > @@ -2731,9 +2729,6 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm) > int vclock_mode; > bool host_tsc_clocksource, vcpus_matched; > > - vcpus_matched = (ka->nr_vcpus_matched_tsc + 1 == > - atomic_read(&kvm->online_vcpus)); > - > /* > * If the host uses TSC clock, then passthrough TSC as stable > * to the guest. > @@ -2742,6 +2737,10 @@ static void pvclock_update_vm_gtod_copy(struct kvm > *kvm) > &ka->master_kernel_ns, > &ka->master_cycle_now); > > + lockdep_assert_held(&kvm->arch.tsc_write_lock); > + vcpus_matched = (ka->nr_vcpus_matched_tsc + 1 == > + atomic_read(&kvm->online_vcpus)); > + > ka->use_master_clock = host_tsc_clocksource && vcpus_matched > && !ka->backwards_tsc_observed > && !ka->boot_vcpu_runs_old_kvmclock; > @@ -2760,14 +2759,18 @@ static void kvm_make_mclock_inprogress_request(struct > kvm *kvm) > kvm_make_all_cpus_request(kvm, KVM_REQ_MCLOCK_INPROGRESS); > } > > -static void kvm_start_pvclock_update(struct kvm *kvm) > +static void __kvm_start_pvclock_update(struct kvm *kvm) > { > - struct kvm_arch *ka = &kvm->arch; > + raw_spin_lock_irq(&kvm->arch.tsc_write_lock); > + write_seqcount_begin(&kvm->arch.pvclock_sc); > +} > > +static void kvm_start_pvclock_update(struct kvm *kvm) > +{ > kvm_make_mclock_inprogress_request(kvm); > > /* no guest entries from this point */ > - spin_lock_irq(&ka->pvclock_gtod_sync_lock); > + __kvm_start_pvclock_update(kvm); > } > > static void kvm_end_pvclock_update(struct kvm *kvm) > @@ -2776,7 +2779,8 @@ static void kvm_end_pvclock_update(struct kvm *kvm) > struct kvm_vcpu *vcpu; > int i; > > - spin_unlock_irq(&ka->pvclock_gtod_sync_lock); > + write_seqcount_end(&ka->pvclock_sc); > + raw_spin_unlock_irq(&ka->tsc_write_lock); > kvm_for_each_vcpu(i, vcpu, kvm) > kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); > > @@ -2797,20 +2801,12 @@ static void get_kvmclock(struct kvm *kvm, struct > kvm_clock_data *data) > { > struct kvm_arch *ka = &kvm->arch; > struct pvclock_vcpu_time_info hv_clock; > - unsigned long flags; > > - spin_lock_irqsave(&ka->pvclock_gtod_sync_lock, flags); > if (!ka->use_master_clock) { > - spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags); > data->clock = get_kvmclock_base_ns() + ka->kvmclock_offset; > return; > } > > - data->flags |= KVM_CLOCK_TSC_STABLE; > - hv_clock.tsc_timestamp = ka->master_cycle_now; > - hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset; > - spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags); > - > /* both __this_cpu_read() and rdtsc() should be on the same cpu */ > get_cpu(); > > @@ -2825,6 +2821,9 @@ static void get_kvmclock(struct kvm *kvm, struct > kvm_clock_data *data) > #endif > data->host_tsc = rdtsc(); > > + data->flags |= KVM_CLOCK_TSC_STABLE; > + hv_clock.tsc_timestamp = ka->master_cycle_now; > + hv_clock.system_time = ka->master_kernel_ns + > ka->kvmclock_offset; > kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * > 1000LL, > &hv_clock.tsc_shift, > &hv_clock.tsc_to_system_mul); > @@ -2839,14 +2838,14 @@ static void get_kvmclock(struct kvm *kvm, struct > kvm_clock_data *data) > u64 get_kvmclock_ns(struct kvm *kvm) > { > struct kvm_clock_data data; > + struct kvm_arch *ka = &kvm->arch; > + unsigned seq; > > - /* > - * Zero flags as it's accessed RMW, leave everything else uninitialized > - * as clock is always written and no other fields are consumed. > - */ > - data.flags = 0; > - > - get_kvmclock(kvm, &data); > + do { > + seq = read_seqcount_begin(&ka->pvclock_sc); > + data.flags = 0; > + get_kvmclock(kvm, &data); > + } while (read_seqcount_retry(&ka->pvclock_sc, seq)); > return data.clock; > } > > @@ -2912,6 +2911,7 @@ static void kvm_setup_pvclock_page(struct kvm_vcpu *v, > static int kvm_guest_time_update(struct kvm_vcpu *v) > { > unsigned long flags, tgt_tsc_khz; > + unsigned seq; > struct kvm_vcpu_arch *vcpu = &v->arch; > struct kvm_arch *ka = &v->kvm->arch; > s64 kernel_ns; > @@ -2926,13 +2926,14 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) > * If the host uses TSC clock, then passthrough TSC as stable > * to the guest. > */ > - spin_lock_irqsave(&ka->pvclock_gtod_sync_lock, flags); > - use_master_clock = ka->use_master_clock; > - if (use_master_clock) { > - host_tsc = ka->master_cycle_now; > - kernel_ns = ka->master_kernel_ns; > - } > - spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags); > + seq = read_seqcount_begin(&ka->pvclock_sc); > + do { > + use_master_clock = ka->use_master_clock; > + if (use_master_clock) { > + host_tsc = ka->master_cycle_now; > + kernel_ns = ka->master_kernel_ns; > + } > + } while (read_seqcount_retry(&ka->pvclock_sc, seq)); > > /* Keep irq disabled to prevent changes to the clock */ > local_irq_save(flags); > @@ -5855,10 +5856,15 @@ int kvm_arch_pm_notifier(struct kvm *kvm, unsigned > long state) > > static int kvm_vm_ioctl_get_clock(struct kvm *kvm, void __user *argp) > { > - struct kvm_clock_data data; > + struct kvm_clock_data data = { 0 }; > + unsigned seq; > + > + do { > + seq = read_seqcount_begin(&kvm->arch.pvclock_sc); > + data.flags = 0; > + get_kvmclock(kvm, &data); > + } while (read_seqcount_retry(&kvm->arch.pvclock_sc, seq)); > > - memset(&data, 0, sizeof(data)); > - get_kvmclock(kvm, &data); > if (copy_to_user(argp, &data, sizeof(data))) > return -EFAULT; > > @@ -8159,9 +8165,7 @@ static void kvm_hyperv_tsc_notifier(void) > kvm_max_guest_tsc_khz = tsc_khz; > > list_for_each_entry(kvm, &vm_list, vm_list) { > - struct kvm_arch *ka = &kvm->arch; > - > - spin_lock_irq(&ka->pvclock_gtod_sync_lock); > + __kvm_start_pvclock_update(kvm); > pvclock_update_vm_gtod_copy(kvm); > kvm_end_pvclock_update(kvm); > } > @@ -11188,8 +11192,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long > type) > > raw_spin_lock_init(&kvm->arch.tsc_write_lock); > mutex_init(&kvm->arch.apic_map_lock); > - spin_lock_init(&kvm->arch.pvclock_gtod_sync_lock); > - > + seqcount_raw_spinlock_init(&kvm->arch.pvclock_sc, > &kvm->arch.tsc_write_lock); > kvm->arch.kvmclock_offset = -get_kvmclock_base_ns(); > pvclock_update_vm_gtod_copy(kvm); > > -- > 2.33.0.309.g3052b89438-goog > >
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