On Mon, Mar 17, 2025, Liam Ni wrote: > When using the dump-guest-memory command in QEMU to dump > the virtual machine's memory,the virtual machine will be > paused for a period of time.If the guest (i.e., UEFI) uses > the PIT as the system clock,it will be observed that the > HRTIMER used by the PIT continues to run during the guest > stop process, imposing an additional burden on the system. > Moreover, during the guest restart process,the previously > established HRTIMER will be canceled,and the accumulated > timer events will be flushed.However, before the old > HRTIMER is canceled,the accumulated timer events > will "surreptitiously" inject interrupts into the guest. > > SO during the process of saving the KVM PIT state, > the HRTIMER need to be canceled to reduce the performance overhead > caused by HRTIMER during the guest stop process. > > i.e. if guest > > Signed-off-by: Liam Ni <liamni-oc@xxxxxxxxxxx> > --- > arch/x86/kvm/x86.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 045c61cc7e54..75355b315aca 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -6405,6 +6405,8 @@ static int kvm_vm_ioctl_get_pit(struct kvm *kvm, struct kvm_pit_state *ps) > > mutex_lock(&kps->lock); > memcpy(ps, &kps->channels, sizeof(*ps)); > + hrtimer_cancel(&kvm->arch.vpit->pit_state.timer); > + kthread_flush_work(&kvm->arch.vpit->expired); KVM cannot assume userspace wants to stop the PIT when grabbing a snapshot. It's a significant ABI change, and not desirable in all cases. > mutex_unlock(&kps->lock); > return 0; > } > @@ -6428,6 +6430,8 @@ static int kvm_vm_ioctl_get_pit2(struct kvm *kvm, struct kvm_pit_state2 *ps) > memcpy(ps->channels, &kvm->arch.vpit->pit_state.channels, > sizeof(ps->channels)); > ps->flags = kvm->arch.vpit->pit_state.flags; > + hrtimer_cancel(&kvm->arch.vpit->pit_state.timer); > + kthread_flush_work(&kvm->arch.vpit->expired); > mutex_unlock(&kvm->arch.vpit->pit_state.lock); > memset(&ps->reserved, 0, sizeof(ps->reserved)); > return 0; > -- > 2.25.1 >
