fix a bug: UOS could hung after running some time.

soft-lock or CPUs stalls can happen during UOS running; after debugging,
find CPUs for UOS is in idle thread, and will not be scheduled back.

root cause: PIO/MMIO from UOS will trigger SOS/DM to handle them. Usually,
it should make sure UOS-vcpu pause first then resume, but for SOS/UOS in
parallel,in former code, the UOS-vcpu resume could be called first by SOS
before pause.

Signed-off-by: Minggui Cao <minggui.cao@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

Author: mgcao

hypervisor/common/io_request.c

@@ -74,6 +74,13 @@ int acrn_insert_request_wait(struct vcpu *vcpu, struct vhm_request *req)
 	memcpy_s(&req_buf->req_queue[cur], sizeof(struct vhm_request),
 		 req, sizeof(struct vhm_request));
 
+	/* pause vcpu, wait for VHM to handle the MMIO request.
+	 * TODO: when pause_vcpu changed to switch vcpu out directlly, we
+	 * should fix the race issue between req.valid = true and vcpu pause
+	 */
+	atomic_store(&vcpu->ioreq_pending, 1);
+	pause_vcpu(vcpu, VCPU_PAUSED);
+
 	/* Must clear the signal before we mark req valid
 	 * Once we mark to valid, VHM may process req and signal us
 	 * before we perform upcall.
@@ -86,10 +93,6 @@ int acrn_insert_request_wait(struct vcpu *vcpu, struct vhm_request *req)
 	/* signal VHM */
 	fire_vhm_interrupt();
 
-	/* pause vcpu, wait for VHM to handle the MMIO request */
-	atomic_store(&vcpu->ioreq_pending, 1);
-	pause_vcpu(vcpu, VCPU_PAUSED);
-
 	return 0;
 }