From: David Woodhouse <[email protected]> The remaining users of pvclock_gtod_data only need to know whether the host clocksource is TSC-based. Cache the vclock_mode value in a simple kvm_host_vclock_mode variable, updated by the pvclock_gtod_notify callback, and use gtod_is_based_on_tsc() for eligibility checks.
This is inherently racy (as it always was — kvm_track_tsc_matching never held the gtod seqcount), relying on eventual consistency: the notifier fires on every timekeeping update and will correct any transient inconsistency within one tick. Signed-off-by: David Woodhouse <[email protected]> Assisted-by: Kiro (claude-opus-4.6-1m) --- arch/x86/kvm/x86.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 8d520bfae089..c67655f8e078 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2647,6 +2647,8 @@ static u64 compute_guest_tsc(struct kvm_vcpu *vcpu, s64 kernel_ns) } #ifdef CONFIG_X86_64 +static int kvm_host_vclock_mode; + static inline bool gtod_is_based_on_tsc(int mode) { return mode == VDSO_CLOCKMODE_TSC || mode == VDSO_CLOCKMODE_HVCLOCK; @@ -2676,7 +2678,6 @@ static bool kvm_use_master_clock(struct kvm *kvm) static void kvm_track_tsc_matching(struct kvm_vcpu *vcpu, bool update_mclock) { struct kvm_arch *ka = &vcpu->kvm->arch; - struct pvclock_gtod_data *gtod = &pvclock_gtod_data; bool prev_matched_tsc = ka->all_vcpus_matched_tsc; /* @@ -2713,7 +2714,7 @@ static void kvm_track_tsc_matching(struct kvm_vcpu *vcpu, bool update_mclock) * accounts for its offset. */ bool use_master_clock = kvm_use_master_clock(vcpu->kvm) && - gtod_is_based_on_tsc(gtod->clock.vclock_mode); + gtod_is_based_on_tsc(kvm_host_vclock_mode); /* * Request a masterclock update if needed: toggling master clock, @@ -2726,11 +2727,11 @@ static void kvm_track_tsc_matching(struct kvm_vcpu *vcpu, bool update_mclock) trace_kvm_track_tsc(vcpu->vcpu_id, ka->nr_vcpus_matched_tsc, atomic_read(&vcpu->kvm->online_vcpus), - ka->use_master_clock, gtod->clock.vclock_mode); + ka->use_master_clock, kvm_host_vclock_mode); } #else static inline void kvm_track_tsc_matching(struct kvm_vcpu *vcpu, - bool new_generation) {} + bool update_mclock) {} #endif /* @@ -2850,7 +2851,7 @@ static inline bool kvm_check_tsc_unstable(void) * TSC is marked unstable when we're running on Hyper-V, * 'TSC page' clocksource is good. */ - if (pvclock_gtod_data.clock.vclock_mode == VDSO_CLOCKMODE_HVCLOCK) + if (kvm_host_vclock_mode == VDSO_CLOCKMODE_HVCLOCK) return false; #endif return check_tsc_unstable(); @@ -3274,7 +3275,6 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm) { #ifdef CONFIG_X86_64 struct kvm_arch *ka = &kvm->arch; - int vclock_mode; bool host_tsc_clocksource; lockdep_assert_held(&kvm->arch.tsc_write_lock); @@ -3314,9 +3314,9 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm) ka->use_master_clock = false; } - vclock_mode = pvclock_gtod_data.clock.vclock_mode; - trace_kvm_update_master_clock(ka->use_master_clock, vclock_mode, - ka->all_vcpus_matched_freq); + trace_kvm_update_master_clock(ka->use_master_clock, + kvm_host_vclock_mode, + ka->all_vcpus_matched_freq); #endif } @@ -10399,12 +10399,15 @@ static int pvclock_gtod_notify(struct notifier_block *nb, unsigned long unused, update_pvclock_gtod(tk); #ifdef CONFIG_X86_64 + kvm_host_vclock_mode = + tk->tkr_mono.clock->vdso_clock_mode; + /* * Disable master clock if host does not trust, or does not use, * TSC based clocksource. Delegate queue_work() to irq_work as * this is invoked with tk_core.seq write held. */ - if (!gtod_is_based_on_tsc(pvclock_gtod_data.clock.vclock_mode) && + if (!gtod_is_based_on_tsc(kvm_host_vclock_mode) && atomic_read(&kvm_guest_has_master_clock) != 0) irq_work_queue(&pvclock_irq_work); #endif -- 2.54.0
