s390/cpacf: Make use of invalid opcode produce a link error

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From: Harald Freudenberger <freude@xxxxxxxxxxxxx>

commit 32e8bd6423fc127d2b37bdcf804fd76af3bbec79 upstream.

Instead of calling BUG() at runtime introduce and use a prototype for a
non-existing function to produce a link error during compile when a not
supported opcode is used with the __cpacf_query() or __cpacf_check_opcode()
inline functions.

Suggested-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
Signed-off-by: Harald Freudenberger <freude@xxxxxxxxxxxxx>
Reviewed-by: Holger Dengler <dengler@xxxxxxxxxxxxx>
Reviewed-by: Juergen Christ <jchrist@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/s390/include/asm/cpacf.h |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/arch/s390/include/asm/cpacf.h
+++ b/arch/s390/include/asm/cpacf.h
@@ -161,6 +161,13 @@
 
 typedef struct { unsigned char bytes[16]; } cpacf_mask_t;
 
+/*
+ * Prototype for a not existing function to produce a link
+ * error if __cpacf_query() or __cpacf_check_opcode() is used
+ * with an invalid compile time const opcode.
+ */
+void __cpacf_bad_opcode(void);
+
 static __always_inline void __cpacf_query_rre(u32 opc, u8 r1, u8 r2,
 					      cpacf_mask_t *mask)
 {
@@ -232,7 +239,7 @@ static __always_inline void __cpacf_quer
 		__cpacf_query_rre(CPACF_PRNO, 2, 4, mask);
 		break;
 	default:
-		BUG();
+		__cpacf_bad_opcode();
 	}
 }
 
@@ -257,7 +264,8 @@ static __always_inline int __cpacf_check
 	case CPACF_KMA:
 		return test_facility(146);	/* check for MSA8 */
 	default:
-		BUG();
+		__cpacf_bad_opcode();
+		return 0;
 	}
 }
 


Patches currently in stable-queue which might be from freude@xxxxxxxxxxxxx are

queue-5.15/s390-ap-fix-crash-in-ap-internal-function-modify_bitmap.patch
queue-5.15/s390-cpacf-make-use-of-invalid-opcode-produce-a-link-error.patch
queue-5.15/s390-cpacf-split-and-rework-cpacf-query-functions.patch




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