KVM: PPC: Book3S PR: Avoid changing TS bits when exiting guest

PR KVM host usually runs with TM enabled in its host MSR value, and
with non-transactional TS value.

When a guest with TM active traps into PR KVM host, the rfid at the
tail of kvmppc_interrupt_pr() will try to switch TS bits from
S0 (Suspended & TM disabled) to N1 (Non-transactional & TM enabled).

That will leads to TM Bad Thing interrupt.

This patch manually sets target TS bits unchanged to avoid this
exception.
Signed-off-by: Simon Guo <wei.guo.simon@gmail.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_segment.S

@@ -383,6 +383,19 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 	 */
 
 	PPC_LL	r6, HSTATE_HOST_MSR(r13)
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+	/*
+	 * We don't want to change MSR[TS] bits via rfi here.
+	 * The actual TM handling logic will be in host with
+	 * recovered DR/IR bits after HSTATE_VMHANDLER.
+	 * And MSR_TM can be enabled in HOST_MSR so rfid may
+	 * not suppress this change and can lead to exception.
+	 * Manually set MSR to prevent TS state change here.
+	 */
+	mfmsr   r7
+	rldicl  r7, r7, 64 - MSR_TS_S_LG, 62
+	rldimi  r6, r7, MSR_TS_S_LG, 63 - MSR_TS_T_LG
+#endif
 	PPC_LL	r8, HSTATE_VMHANDLER(r13)
 
 #ifdef CONFIG_PPC64