From: David Matlack <dmatlack@xxxxxxxxxx>
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: David Matlack <dmatlack@xxxxxxxxxx>
Signed-off-by: Jon Cargille <jcargill@xxxxxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 17 +++++++++++++++++
include/linux/kvm_host.h | 1 +
include/uapi/linux/kvm.h | 1 +
virt/kvm/kvm_main.c | 19 +++++++++++++++----
4 files changed, 34 insertions(+), 4 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index efbbe570aa9b7b..d871dacb984e98 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -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.
======================
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 6d58beb65454f7..922b24ce5e7297 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -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, ...) \
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 428c7dde6b4b37..ac9eba0289d1b6 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -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
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 74bdb7bf32952e..ec038a9e60a275 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -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;
@@ -2716,15 +2718,16 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
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;
@@ -3516,6 +3519,7 @@ 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:
@@ -3566,6 +3570,13 @@ 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);
}
--
2.26.1.301.g55bc3eb7cb9-goog
