KVM: grow_halt_poll_ns() should never shrink vCPU halt_poll_ns

grow_halt_poll_ns() have a strange behavior in case
(halt_poll_ns_grow == 0) && (vcpu->halt_poll_ns != 0).

In this case, vcpu->halt_pol_ns will be set to zero.
That results in shrinking instead of growing.

Fix issue by changing grow_halt_poll_ns() to not modify
vcpu->halt_poll_ns in case halt_poll_ns_grow is zero

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Nir Weiner <nir.weiner@oracle.com>
Suggested-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 5a066fc..e316a2d 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3631,8 +3631,11 @@ static void kvmppc_wait_for_exec(struct kvmppc_vcore *vc,
 
 static void grow_halt_poll_ns(struct kvmppc_vcore *vc)
 {
+       if (!halt_poll_ns_grow)
+               return;
+
        /* 10us base */
-       if (vc->halt_poll_ns == 0 && halt_poll_ns_grow)
+       if (vc->halt_poll_ns == 0)
                vc->halt_poll_ns = 10000;
        else
                vc->halt_poll_ns *= halt_poll_ns_grow;

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c9d0bc0..9c8a8bf 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2188,8 +2188,11 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 
        old = val = vcpu->halt_poll_ns;
        grow = READ_ONCE(halt_poll_ns_grow);
+       if (!grow)
+               goto out;
+
        /* 10us base */
-       if (val == 0 && grow)
+       if (val == 0)
                val = 10000;
        else
                val *= grow;
@@ -2198,6 +2201,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
                val = halt_poll_ns;
 
        vcpu->halt_poll_ns = val;
+out:
        trace_kvm_halt_poll_ns_grow(vcpu->vcpu_id, val, old);
 }