powerpc/perf: Avoid spurious PMU interrupts after idle

POWER9 DD2 can see spurious PMU interrupts after state-loss idle in
some conditions.

A solution is to save and reload MMCR0 over state-loss idle.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Tested-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/idle_book3s.S

@@ -30,6 +30,7 @@
  * Use unused space in the interrupt stack to save and restore
  * registers for winkle support.
  */
+#define _MMCR0	GPR0
 #define _SDR1	GPR3
 #define _PTCR	GPR3
 #define _RPR	GPR4
@@ -272,6 +273,14 @@ power_enter_stop:
 	b 	pnv_wakeup_noloss
 
 .Lhandle_esl_ec_set:
+	/*
+	 * POWER9 DD2 can incorrectly set PMAO when waking up after a
+	 * state-loss idle. Saving and restoring MMCR0 over idle is a
+	 * workaround.
+	 */
+	mfspr	r4,SPRN_MMCR0
+	std	r4,_MMCR0(r1)
+
 /*
  * Check if the requested state is a deep idle state.
  */
@@ -450,10 +459,14 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_300)
 pnv_restore_hyp_resource_arch300:
 	/*
 	 * Workaround for POWER9, if we lost resources, the ERAT
-	 * might have been mixed up and needs flushing.
+	 * might have been mixed up and needs flushing. We also need
+	 * to reload MMCR0 (see comment above).
 	 */
 	blt	cr3,1f
 	PPC_INVALIDATE_ERAT
+	ld	r1,PACAR1(r13)
+	ld	r4,_MMCR0(r1)
+	mtspr	SPRN_MMCR0,r4
 1:
 	/*
 	 * POWER ISA 3. Use PSSCR to determine if we