Subject: [PATCH] Fix "[v3, 28/32] powerpc/64s: interrupt implement exit logic in C"

From: Nicholas Piggin <[email-masked]>
Date: Thu, 19 Mar 2020 16:59:34 +1000

Accessing thread_info flags can cause an SLB fault, so it must not
be done with MSR[RI]=0, which leads to SLB unrecoverable fault error.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kernel/syscall_64.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kernel/syscall_64.c b/arch/powerpc/kernel/syscall_64.c
index 87d95b455b83..a56ae78f2d1d 100644
--- a/arch/powerpc/kernel/syscall_64.c
+++ b/arch/powerpc/kernel/syscall_64.c
@@ -313,12 +313,18 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsign
 {
 	unsigned long *ti_flagsp = &current_thread_info()->flags;
 	unsigned long flags;
+	unsigned long ret = 0;
 
 	if (IS_ENABLED(CONFIG_PPC_BOOK3S) && unlikely(!(regs->msr & MSR_RI)))
 		unrecoverable_exception(regs);
 	BUG_ON(regs->msr & MSR_PR);
 	BUG_ON(!FULL_REGS(regs));
 
+	if (unlikely(*ti_flagsp & _TIF_EMULATE_STACK_STORE)) {
+		clear_bits(_TIF_EMULATE_STACK_STORE, ti_flagsp);
+		ret = 1;
+	}
+
 	local_irq_save(flags);
 
 	if (regs->softe == IRQS_ENABLED) {
@@ -370,10 +376,6 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsign
 	 */
 	kuap_restore_amr(regs);
 
-	if (unlikely(*ti_flagsp & _TIF_EMULATE_STACK_STORE)) {
-		clear_bits(_TIF_EMULATE_STACK_STORE, ti_flagsp);
-		return 1;
-	}
-	return 0;
+	return ret;
 }
 #endif
-- 
2.23.0