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KVM: Obey kvm.halt_poll_ns in VMs not using KVM_CAP_HALT_POLL

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Obey kvm.halt_poll_ns in VMs not using KVM_CAP_HALT_POLL on every halt,
rather than just sampling the module parameter when the VM is first
created. This restore the original behavior of kvm.halt_poll_ns for VMs
that have not opted into KVM_CAP_HALT_POLL.

Notably, this change restores the ability for admins to disable or
change the maximum halt-polling time system wide for VMs not using
KVM_CAP_HALT_POLL.

Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Fixes: acd05785e4 ("kvm: add capability for halt polling")
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20221117001657.1067231-4-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
David Matlack 2022-11-16 16:16:57 -08:00 committed by Paolo Bonzini
parent 175d5dc79d
commit 9eb8ca049c
2 changed files with 25 additions and 3 deletions
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1
include/linux/kvm_host.h
View File

@ -776,6 +776,7 @@ struct kvm {
struct srcu_struct srcu;
struct srcu_struct irq_srcu;
pid_t userspace_pid;
bool override_halt_poll_ns;
unsigned int max_halt_poll_ns;
u32 dirty_ring_size;
bool vm_bugged;

27
virt/kvm/kvm_main.c
View File

@ -1198,8 +1198,6 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
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;
@ -3482,7 +3480,20 @@ static inline void update_halt_poll_stats(struct kvm_vcpu *vcpu, ktime_t start,
static unsigned int kvm_vcpu_max_halt_poll_ns(struct kvm_vcpu *vcpu)
{
return READ_ONCE(vcpu->kvm->max_halt_poll_ns);
struct kvm *kvm = vcpu->kvm;
if (kvm->override_halt_poll_ns) {
/*
* Ensure kvm->max_halt_poll_ns is not read before
* kvm->override_halt_poll_ns.
*
* Pairs with the smp_wmb() when enabling KVM_CAP_HALT_POLL.
*/
smp_rmb();
return READ_ONCE(kvm->max_halt_poll_ns);
}
return READ_ONCE(halt_poll_ns);
}
/*
@ -4592,6 +4603,16 @@ static int kvm_vm_ioctl_enable_cap_generic(struct kvm *kvm,
return -EINVAL;
kvm->max_halt_poll_ns = cap->args[0];
/*
* Ensure kvm->override_halt_poll_ns does not become visible
* before kvm->max_halt_poll_ns.
*
* Pairs with the smp_rmb() in kvm_vcpu_max_halt_poll_ns().
*/
smp_wmb();
kvm->override_halt_poll_ns = true;
return 0;
}
case KVM_CAP_DIRTY_LOG_RING: