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kvm: add capability for halt polling

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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@google.com>
Signed-off-by: Jon Cargille <jcargill@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Message-Id: <20200417221446.108733-1-jcargill@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
David Matlack 2020-04-17 15:14:46 -07:00 committed by Paolo Bonzini
parent 87796555d4
commit acd05785e4
4 changed files with 34 additions and 4 deletions
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17
Documentation/virt/kvm/api.rst
View File

@ -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.
======================

1
include/linux/kvm_host.h
View File

@ -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, ...) \

1
include/uapi/linux/kvm.h
View File

@ -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

19
virt/kvm/kvm_main.c
View File

@ -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);
}