commit 785dbef407d8 ("KVM: s390: optimize round trip time in request
handling") introduced a regression. This regression was seen with
CPU hotplug in the guest and switching between 1 or 2 CPUs. This will
set/reset the IBS control via synced request.Whenever we make a synced request, we first set the vcpu->requests bit and then block the vcpu. The handler, on the other hand, unblocks itself, processes vcpu->requests (by clearing them) and unblocks itself once again. Now, if the requester sleeps between setting of vcpu->requests and blocking, the handler will clear the vcpu->requests bit and try to unblock itself (although no bit is set). When the requester wakes up, it blocks the VCPU and we have a blocked VCPU without requests. Solution is to always unset the block bit. Signed-off-by: Christian Borntraeger <[email protected]> Reviewed-by: David Hildenbrand <[email protected]> Fixes: 785dbef407d8 ("KVM: s390: optimize round trip time in request handling") --- arch/s390/kvm/kvm-s390.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 2078f92..f32f843 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -1742,10 +1742,10 @@ static bool ibs_enabled(struct kvm_vcpu *vcpu) static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu) { - if (!vcpu->requests) - return 0; retry: kvm_s390_vcpu_request_handled(vcpu); + if (!vcpu->requests) + return 0; /* * We use MMU_RELOAD just to re-arm the ipte notifier for the * guest prefix page. gmap_ipte_notify will wait on the ptl lock. -- 2.3.0 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
