powerpc/64s: system call avoid setting MSR[RI] until we set MSR[EE]

This extends the MSR[RI]=0 window a little further into the system
call in order to pair RI and EE enabling with a single mtmsrd.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-8-npiggin@gmail.com

Author: npiggin

arch/powerpc/kernel/exceptions-64s.S

@@ -1861,8 +1861,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE)
 	mtctr	r10
 	bctr
 	.else
-	li	r10,MSR_RI
-	mtmsrd 	r10,1			/* Set RI (EE=0) */
 #ifdef CONFIG_RELOCATABLE
 	__LOAD_HANDLER(r10, system_call_common)
 	mtctr	r10

arch/powerpc/kernel/interrupt_64.S

@@ -283,9 +283,9 @@ END_BTB_FLUSH_SECTION
 	 * trace_hardirqs_off().
 	 */
 	li	r11,IRQS_ALL_DISABLED
-	li	r12,PACA_IRQ_HARD_DIS
+	li	r12,-1 /* Set MSR_EE and MSR_RI */
 	stb	r11,PACAIRQSOFTMASK(r13)
-	stb	r12,PACAIRQHAPPENED(r13)
+	mtmsrd	r12,1
 
 	/* Calling convention has r9 = orig r0, r10 = regs */
 	mr	r9,r0