Commit acd05785 authored by David Matlack's avatar David Matlack Committed by Paolo Bonzini
Browse files

kvm: add capability for halt polling 



KVM_CAP_HALT_POLL is a per-VM capability that lets userspace
control the halt-polling time, allowing halt-polling to be tuned or
disabled on particular VMs.

With dynamic halt-polling, a VM's VCPUs can poll from anywhere from
[0, halt_poll_ns] on each halt. KVM_CAP_HALT_POLL sets the
upper limit on the poll time.

Signed-off-by: default avatarDavid Matlack <dmatlack@google.com>
Signed-off-by: default avatarJon Cargille <jcargill@google.com>
Reviewed-by: default avatarJim Mattson <jmattson@google.com>
Message-Id: <20200417221446.108733-1-jcargill@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 87796555

Documentation/virt/kvm/api.rst

+17 −0
Original line number Diff line number Diff line
@@ -5802,6 +5802,23 @@ If present, this capability can be enabled for a VM, meaning that KVM 
will allow the transition to secure guest mode.  Otherwise KVM will

veto the transition.



7.20 KVM_CAP_HALT_POLL

----------------------



:Architectures: all

:Target: VM

:Parameters: args[0] is the maximum poll time in nanoseconds

:Returns: 0 on success; -1 on error



This capability overrides the kvm module parameter halt_poll_ns for the

target VM.



VCPU polling allows a VCPU to poll for wakeup events instead of immediately

scheduling during guest halts. The maximum time a VCPU can spend polling is

controlled by the kvm module parameter halt_poll_ns. This capability allows

the maximum halt time to specified on a per-VM basis, effectively overriding

the module parameter for the target VM.



8. Other capabilities.

======================

include/linux/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -503,6 +503,7 @@ struct kvm { 
	struct srcu_struct srcu;

	struct srcu_struct irq_srcu;

	pid_t userspace_pid;

	unsigned int max_halt_poll_ns;

};



#define kvm_err(fmt, ...) \

include/uapi/linux/kvm.h

+1 −0
Original line number Diff line number Diff line
@@ -1017,6 +1017,7 @@ struct kvm_ppc_resize_hpt { 
#define KVM_CAP_S390_VCPU_RESETS 179

#define KVM_CAP_S390_PROTECTED 180

#define KVM_CAP_PPC_SECURE_GUEST 181

#define KVM_CAP_HALT_POLL 182



#ifdef KVM_CAP_IRQ_ROUTING

virt/kvm/kvm_main.c

+15 −4
Original line number Diff line number Diff line
@@ -710,6 +710,8 @@ static struct kvm *kvm_create_vm(unsigned long type) 
			goto out_err_no_arch_destroy_vm;

	}



	kvm->max_halt_poll_ns = halt_poll_ns;



	r = kvm_arch_init_vm(kvm, type);

	if (r)

		goto out_err_no_arch_destroy_vm;
@@ -2713,15 +2715,16 @@ out: 
	if (!kvm_arch_no_poll(vcpu)) {

		if (!vcpu_valid_wakeup(vcpu)) {

			shrink_halt_poll_ns(vcpu);

		} else if (halt_poll_ns) {

		} else if (vcpu->kvm->max_halt_poll_ns) {

			if (block_ns <= vcpu->halt_poll_ns)

				;

			/* we had a long block, shrink polling */

			else if (vcpu->halt_poll_ns && block_ns > halt_poll_ns)

			else if (vcpu->halt_poll_ns &&

					block_ns > vcpu->kvm->max_halt_poll_ns)

				shrink_halt_poll_ns(vcpu);

			/* we had a short halt and our poll time is too small */

			else if (vcpu->halt_poll_ns < halt_poll_ns &&

				block_ns < halt_poll_ns)

			else if (vcpu->halt_poll_ns < vcpu->kvm->max_halt_poll_ns &&

					block_ns < vcpu->kvm->max_halt_poll_ns)

				grow_halt_poll_ns(vcpu);

		} else {

			vcpu->halt_poll_ns = 0;
@@ -3510,6 +3513,7 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) 
	case KVM_CAP_IOEVENTFD_ANY_LENGTH:

	case KVM_CAP_CHECK_EXTENSION_VM:

	case KVM_CAP_ENABLE_CAP_VM:

	case KVM_CAP_HALT_POLL:

		return 1;

#ifdef CONFIG_KVM_MMIO

	case KVM_CAP_COALESCED_MMIO:
@@ -3560,6 +3564,13 @@ static int kvm_vm_ioctl_enable_cap_generic(struct kvm *kvm, 
		return 0;

	}

#endif

	case KVM_CAP_HALT_POLL: {

		if (cap->flags || cap->args[0] != (unsigned int)cap->args[0])

			return -EINVAL;



		kvm->max_halt_poll_ns = cap->args[0];

		return 0;

	}

	default:

		return kvm_vm_ioctl_enable_cap(kvm, cap);

	}

CRA Git | Maintained and supported by SUSTech CRA and CCSE