KVM: PPC: Book3S HV: Don't wake thread with no vcpu on guest IPI

When running a multi-threaded guest and vcpu 0 in a virtual core
is not running in the guest (i.e. it is busy elsewhere in the host),
thread 0 of the physical core will switch the MMU to the guest and
then go to nap mode in the code at kvm_do_nap.  If the guest sends
an IPI to thread 0 using the msgsndp instruction, that will wake
up thread 0 and cause all the threads in the guest to exit to the
host unnecessarily.  To avoid the unnecessary exit, this arranges
for the PECEDP bit to be cleared in this situation.  When napping
due to a H_CEDE from the guest, we still set PECEDP so that the
thread will wake up on an IPI sent using msgsndp.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -191,6 +191,7 @@ kvmppc_primary_no_guest:
 	li	r3, NAPPING_NOVCPU
 	stb	r3, HSTATE_NAPPING(r13)
 
+	li	r3, 0		/* Don't wake on privileged (OS) doorbell */
 	b	kvm_do_nap
 
 kvm_novcpu_wakeup:
@@ -2129,10 +2130,13 @@ _GLOBAL(kvmppc_h_cede)		/* r3 = vcpu pointer, r11 = msr, r13 = paca */
 	bl	kvmhv_accumulate_time
 #endif
 
+	lis	r3, LPCR_PECEDP@h	/* Do wake on privileged doorbell */
+
 	/*
 	 * Take a nap until a decrementer or external or doobell interrupt
-	 * occurs, with PECE1, PECE0 and PECEDP set in LPCR. Also clear the
-	 * runlatch bit before napping.
+	 * occurs, with PECE1 and PECE0 set in LPCR.
+	 * On POWER8, if we are ceding, also set PECEDP.
+	 * Also clear the runlatch bit before napping.
 	 */
 kvm_do_nap:
 	mfspr	r0, SPRN_CTRLF
@@ -2144,7 +2148,7 @@ kvm_do_nap:
 	mfspr	r5,SPRN_LPCR
 	ori	r5,r5,LPCR_PECE0 | LPCR_PECE1
 BEGIN_FTR_SECTION
-	oris	r5,r5,LPCR_PECEDP@h
+	rlwimi	r5, r3, 0, LPCR_PECEDP
 END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	mtspr	SPRN_LPCR,r5
 	isync