KVM: arm64: Add helpers for ESR_ELx_ERET_ISS_ERET*

The ESR_ELx_ERET_ISS_ERET* macros are a bit confusing:

- ESR_ELx_ERET_ISS_ERET really indicates that we have trapped an
  ERETA* instruction, as opposed to an ERET

- ESR_ELx_ERET_ISS_ERETA really indicates that we have trapped
  an ERETAB instruction, as opposed to an ERETAA.

We could repaint those to make more sense, but these are the
names that are present in the ARM ARM, and we are sentimentally
attached to those.

Instead, add two new helpers:

- esr_iss_is_eretax() being true tells you that you need to
  authenticate the ERET

- esr_iss_is_eretab() tells you that you need to use the B key
  instead of the A key

Following patches will make use of these primitives.

Suggested-by: Joey Gouly <joey.gouly@arm.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240419102935.1935571-3-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/esr.h

@@ -404,6 +404,18 @@ static inline bool esr_fsc_is_access_flag_fault(unsigned long esr)
 	return (esr & ESR_ELx_FSC_TYPE) == ESR_ELx_FSC_ACCESS;
 }
 
+/* Indicate whether ESR.EC==0x1A is for an ERETAx instruction */
+static inline bool esr_iss_is_eretax(unsigned long esr)
+{
+	return esr & ESR_ELx_ERET_ISS_ERET;
+}
+
+/* Indicate which key is used for ERETAx (false: A-Key, true: B-Key) */
+static inline bool esr_iss_is_eretab(unsigned long esr)
+{
+	return esr & ESR_ELx_ERET_ISS_ERETA;
+}
+
 const char *esr_get_class_string(unsigned long esr);
 #endif /* __ASSEMBLY */
 

arch/arm64/kvm/handle_exit.c

@@ -219,7 +219,7 @@ static int kvm_handle_ptrauth(struct kvm_vcpu *vcpu)
 
 static int kvm_handle_eret(struct kvm_vcpu *vcpu)
 {
-	if (kvm_vcpu_get_esr(vcpu) & ESR_ELx_ERET_ISS_ERET)
+	if (esr_iss_is_eretax(kvm_vcpu_get_esr(vcpu)))
 		return kvm_handle_ptrauth(vcpu);
 
 	/*