Subject: [PATCH] powerpc/64s/radix: Fix radix segment exception handling

From: Nicholas Piggin <[email-masked]>
Date: Fri, 29 Mar 2019 17:42:57 +1000

Commit 48e7b76957 ("powerpc/64s/hash: Convert SLB miss handlers to C")
broke the radix-mode segment exception handler. In radix mode, this is
exception is not an SLB miss, rather it signals that the EA is outside
the range translated by any page table.

The commit lost the radix feature alternate code patch, which can
cause faults to some EAs to kernel BUG at arch/powerpc/mm/slb.c:639!

The original radix code would send faults to slb_miss_large_addr,
which would end up faulting due to slb_addr_limit being 0. This patch
sends radix directly to do_bad_slb_fault, which is a bit clearer.

Fixes: 48e7b76957 ("powerpc/64s/hash: Convert SLB miss handlers to C")
Cc: Aneesh Kumar K.V <[email-masked]>
Reported-by: Anton Blanchard <[email-masked]>
Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kernel/exceptions-64s.S | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index a5b8fbae56a0..9481a117e242 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -656,11 +656,17 @@ EXC_COMMON_BEGIN(data_access_slb_common)
 	ld	r4,PACA_EXSLB+EX_DAR(r13)
 	std	r4,_DAR(r1)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
+BEGIN_MMU_FTR_SECTION
+	/* HPT case, do SLB fault */
 	bl	do_slb_fault
 	cmpdi	r3,0
 	bne-	1f
 	b	fast_exception_return
 1:	/* Error case */
+MMU_FTR_SECTION_ELSE
+	/* Radix case, access is outside page table range */
+	li	r3,-EFAULT
+ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
 	std	r3,RESULT(r1)
 	bl	save_nvgprs
 	RECONCILE_IRQ_STATE(r10, r11)
@@ -705,11 +711,17 @@ EXC_COMMON_BEGIN(instruction_access_slb_common)
 	EXCEPTION_PROLOG_COMMON(0x480, PACA_EXSLB)
 	ld	r4,_NIP(r1)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
+BEGIN_MMU_FTR_SECTION
+	/* HPT case, do SLB fault */
 	bl	do_slb_fault
 	cmpdi	r3,0
 	bne-	1f
 	b	fast_exception_return
 1:	/* Error case */
+MMU_FTR_SECTION_ELSE
+	/* Radix case, access is outside page table range */
+	li	r3,-EFAULT
+ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
 	std	r3,RESULT(r1)
 	bl	save_nvgprs
 	RECONCILE_IRQ_STATE(r10, r11)
-- 
2.20.1