[PATCH v2] powerpc/32: Restore clearing of MSR[RI] at interrupt/syscall exit

[Christophe Leroy]

Commit 13799748b957 ("powerpc/64: use interrupt restart table to speed
up return from interrupt") removed the inconditional clearing of
MSR[RI] when returning from interrupt into kernel. But powerpc/32
doesn't implement interrupt restart table hence still need MSR[RI]
to be cleared.

It could be added back in interrupt_exit_kernel_prepare() but it is
easier and better to add it back in entry_32.S for following reasons:
- Writing to MSR must be followed by a synchronising instruction
- The smaller the non recoverable section is the better it is

So add a macro called clr_ri and use it in the three places that play
up with SRR0/SRR1. Use it just before another mtspr for synchronisation
to avoid having to add an isync.

Now that's done in entry_32.S, exit_must_hard_disable() can return
false for non book3s/64, taking into account that BOOKE doesn't have
MSR_RI.

Also add back blacklisting syscall_exit_finish for kprobe. This was
initially added by commit 7cdf44013885 ("powerpc/entry32: Blacklist
syscall exit points for kprobe.") then lost with
commit 6f76a01173cc ("powerpc/syscall: implement system call
entry/exit logic in C for PPC32").

Fixes: 6f76a01173cc ("powerpc/syscall: implement system call entry/exit logic 
in C for PPC32")
Fixes: 13799748b957 ("powerpc/64: use interrupt restart table to speed up 
return from interrupt")
Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
---
 arch/powerpc/kernel/entry_32.S  | 18 +++++++++++++++++-
 arch/powerpc/kernel/interrupt.c |  2 +-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index c37480176a1c..16f8ee6cb2cd 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -101,6 +101,17 @@ 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)
@@ -149,6 +160,7 @@ ret_from_syscall:
        cmpwi   r3,0
        REST_GPR(3, r1)
 syscall_exit_finish:
+       clr_ri  r4
        mtspr   SPRN_SRR0,r7
        mtspr   SPRN_SRR1,r8
 
@@ -168,6 +180,7 @@ syscall_exit_finish:
        REST_GPR(0, r1)
        REST_GPRS(3, 12, r1)
        b       1b
+_ASM_NOKPROBE_SYMBOL(syscall_exit_finish)
 
 #ifdef CONFIG_44x
 .L44x_icache_flush:
@@ -224,10 +237,11 @@ fast_exception_return:
        /* Clear the exception marker on the stack to avoid confusing 
stacktrace */
        li      r10, 0
        stw     r10, 8(r11)
-       REST_GPR(10, r11)
+       clr_ri  r10
        mtspr   SPRN_SRR1,r9
        mtspr   SPRN_SRR0,r12
        REST_GPR(9, r11)
+       REST_GPR(10, r11)
        REST_GPR(12, r11)
        REST_GPR(11, r11)
        rfi
@@ -256,6 +270,7 @@ 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
 
@@ -298,6 +313,7 @@ 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
 
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index e0c681d0b076..aea6f7e8e9c6 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/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 true;
+       return false;
 }
 #endif
 
-- 
2.49.0