ppc/kvm: Set the runlatch bit of a CPU just before starting guest

The secondary threads in the core are kept offline before launching guests
in kvm on powerpc: "371fefd6f2dc4666:KVM: PPC: Allow book3s_hv guests to use
SMT processor modes."

Hence their runlatch bits are cleared. When the secondary threads are called
in to start a guest, their runlatch bits need to be set to indicate that they
are busy. The primary thread has its runlatch bit set though, but there is no
harm in setting this bit once again. Hence set the runlatch bit for all
threads before they start guest.

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Acked-by: Paul Mackerras <paulus@samba.org>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -242,6 +242,12 @@ kvm_novcpu_exit:
  */
 	.globl	kvm_start_guest
 kvm_start_guest:
+
+	/* Set runlatch bit the minute you wake up from nap */
+	mfspr	r1, SPRN_CTRLF
+	ori 	r1, r1, 1
+	mtspr	SPRN_CTRLT, r1
+
 	ld	r2,PACATOC(r13)
 
 	li	r0,KVM_HWTHREAD_IN_KVM