powerpc/32: Restore disabling of interrupts at interrupt/syscall exit

Commit 2997876 ("powerpc/32: Restore clearing of MSR[RI] at
interrupt/syscall exit") delayed clearing of MSR[RI], but missed that
both MSR[RI] and MSR[EE] are cleared at the same time, so the commit
also delayed the disabling of interrupts, leading to unexpected
behaviour.

To fix that, mostly revert the blamed commit and restore the clearing
of MSR[RI] in interrupt_exit_kernel_prepare() instead. For 8xx it
implies adding a synchronising instruction after the mtspr in order to
make sure no instruction counter interrupt (used for perf events) will
fire just after clearing MSR[RI].

Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Closes: https://lore.kernel.org/all/4d0bd05d-6158-1323-3509-744d3fbe8fc7@xenosoft.de/
Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/all/6b05eb1c-fdef-44e0-91a7-8286825e68f1@roeck-us.net/
Fixes: 2997876 ("powerpc/32: Restore clearing of MSR[RI] at interrupt/syscall exit")
Signed-off-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/585ea521b2be99d293b539bbfae148366cfb3687.1766146895.git.chleroy@kernel.org

Author: Christophe Leroy (CS GROUP)

arch/powerpc/include/asm/hw_irq.h

@@ -90,7 +90,7 @@ static inline void __hard_EE_RI_disable(void)
 	if (IS_ENABLED(CONFIG_BOOKE))
 		wrtee(0);
 	else if (IS_ENABLED(CONFIG_PPC_8xx))
-		wrtspr(SPRN_NRI);
+		wrtspr_sync(SPRN_NRI);
 	else if (IS_ENABLED(CONFIG_PPC_BOOK3S_64))
 		__mtmsrd(0, 1);
 	else

arch/powerpc/include/asm/reg.h

@@ -1400,6 +1400,7 @@ static inline void mtmsr_isync(unsigned long val)
 				     : "r" ((unsigned long)(v)) \
 				     : "memory")
 #define wrtspr(rn)	asm volatile("mtspr " __stringify(rn) ",2" : : : "memory")
+#define wrtspr_sync(rn)	asm volatile("mtspr " __stringify(rn) ",2; sync" : : : "memory")
 
 static inline void wrtee(unsigned long val)
 {

arch/powerpc/kernel/entry_32.S

@@ -101,17 +101,6 @@ SYM_FUNC_END(__kuep_unlock)
 .endm
 #endif
 
-.macro	clr_ri trash
-#ifndef CONFIG_BOOKE
-#ifdef CONFIG_PPC_8xx
-	mtspr   SPRN_NRI, \trash
-#else
-	li	\trash, MSR_KERNEL & ~MSR_RI
-	mtmsr	\trash
-#endif
-#endif
-.endm
-
 	.globl	transfer_to_syscall
 transfer_to_syscall:
 	stw	r3, ORIG_GPR3(r1)
@@ -160,7 +149,6 @@ ret_from_syscall:
 	cmpwi	r3,0
 	REST_GPR(3, r1)
 syscall_exit_finish:
-	clr_ri	r4
 	mtspr	SPRN_SRR0,r7
 	mtspr	SPRN_SRR1,r8
 
@@ -237,7 +225,6 @@ fast_exception_return:
 	/* Clear the exception marker on the stack to avoid confusing stacktrace */
 	li	r10, 0
 	stw	r10, 8(r11)
-	clr_ri	r10
 	mtspr	SPRN_SRR1,r9
 	mtspr	SPRN_SRR0,r12
 	REST_GPR(9, r11)
@@ -270,7 +257,6 @@ interrupt_return:
 .Lfast_user_interrupt_return:
 	lwz	r11,_NIP(r1)
 	lwz	r12,_MSR(r1)
-	clr_ri	r4
 	mtspr	SPRN_SRR0,r11
 	mtspr	SPRN_SRR1,r12
 
@@ -313,7 +299,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
 	cmpwi	cr1,r3,0
 	lwz	r11,_NIP(r1)
 	lwz	r12,_MSR(r1)
-	clr_ri	r4
 	mtspr	SPRN_SRR0,r11
 	mtspr	SPRN_SRR1,r12
 

arch/powerpc/kernel/interrupt.c

@@ -38,7 +38,7 @@ static inline bool exit_must_hard_disable(void)
 #else
 static inline bool exit_must_hard_disable(void)
 {
-	return false;
+	return true;
 }
 #endif
 
@@ -443,6 +443,9 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
 
 		if (unlikely(stack_store))
 			__hard_EE_RI_disable();
+#else
+	} else {
+		__hard_EE_RI_disable();
 #endif /* CONFIG_PPC64 */
 	}