KVM: s390: Fix hang VCPU hang/loop regression
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
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 <firstname.lastname@example.org>
Reviewed-by: David Hildenbrand <email@example.com>
Fixes: 785dbef407d8 ("KVM: s390: optimize round trip time in request handling")
1 file changed