Commit 9eb8ca04 authored by David Matlack's avatar David Matlack Committed by Paolo Bonzini
Browse files

KVM: Obey kvm.halt_poll_ns in VMs not using KVM_CAP_HALT_POLL 



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: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Fixes: acd05785 ("kvm: add capability for halt polling")
Signed-off-by: default avatarDavid Matlack <dmatlack@google.com>
Message-Id: <20221117001657.1067231-4-dmatlack@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 175d5dc7

include/linux/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

virt/kvm/kvm_main.c

+24 −3
Original line number Diff line number Diff line
@@ -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: