arm64: add macro to extract ESR_ELx.EC

Several places open-code extraction of the EC field from an ESR_ELx
value, in subtly different ways. This is unfortunate duplication and
variation, and the precise logic used to extract the field is a
distraction.

This patch adds a new macro, ESR_ELx_EC(), to extract the EC field from
an ESR_ELx value in a consistent fashion.

Existing open-coded extractions in core arm64 code are moved over to the
new helper. KVM code is left as-is for the moment.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Huang Shijie <shijie.huang@arm.com>
Cc: Dave P Martin <dave.martin@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/esr.h

@@ -74,6 +74,7 @@
 
 #define ESR_ELx_EC_SHIFT	(26)
 #define ESR_ELx_EC_MASK		(UL(0x3F) << ESR_ELx_EC_SHIFT)
+#define ESR_ELx_EC(esr)		(((esr) & ESR_ELx_EC_MASK) >> ESR_ELx_EC_SHIFT)
 
 #define ESR_ELx_IL		(UL(1) << 25)
 #define ESR_ELx_ISS_MASK	(ESR_ELx_IL - 1)

arch/arm64/kernel/traps.c

@@ -456,7 +456,7 @@ static const char *esr_class_str[] = {
 
 const char *esr_get_class_string(u32 esr)
 {
-	return esr_class_str[esr >> ESR_ELx_EC_SHIFT];
+	return esr_class_str[ESR_ELx_EC(esr)];
 }
 
 /*

arch/arm64/mm/fault.c

@@ -244,7 +244,7 @@ static int __do_page_fault(struct mm_struct *mm, unsigned long addr,
 
 static inline int permission_fault(unsigned int esr)
 {
-	unsigned int ec       = (esr & ESR_ELx_EC_MASK) >> ESR_ELx_EC_SHIFT;
+	unsigned int ec       = ESR_ELx_EC(esr);
 	unsigned int fsc_type = esr & ESR_ELx_FSC_TYPE;
 
 	return (ec == ESR_ELx_EC_DABT_CUR && fsc_type == ESR_ELx_FSC_PERM);