KVM: arm64: Don't adjust PC on SError during SMC trap

On SMC trap, the prefered return address is set to that of the SMC
instruction itself. It is thus wrong to try and roll it back when
an SError occurs while trapping on SMC. It is still necessary on
HVC though, as HVC doesn't cause a trap, and sets ELR to returning
*after* the HVC.

It also became apparent that there is no 16bit encoding for an AArch32
HVC instruction, meaning that the displacement is always 4 bytes,
no matter what the ISA is. Take this opportunity to simplify it.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/handle_exit.c

@@ -245,15 +245,15 @@ int handle_exit(struct kvm_vcpu *vcpu, int exception_index)
 		u8 esr_ec = ESR_ELx_EC(kvm_vcpu_get_esr(vcpu));
 
 		/*
-		 * HVC/SMC already have an adjusted PC, which we need
-		 * to correct in order to return to after having
-		 * injected the SError.
+		 * HVC already have an adjusted PC, which we need to
+		 * correct in order to return to after having injected
+		 * the SError.
+		 *
+		 * SMC, on the other hand, is *trapped*, meaning its
+		 * preferred return address is the SMC itself.
 		 */
-		if (esr_ec == ESR_ELx_EC_HVC32 || esr_ec == ESR_ELx_EC_HVC64 ||
-		    esr_ec == ESR_ELx_EC_SMC32 || esr_ec == ESR_ELx_EC_SMC64) {
-			u32 adj =  kvm_vcpu_trap_il_is32bit(vcpu) ? 4 : 2;
-			*vcpu_pc(vcpu) -= adj;
-		}
+		if (esr_ec == ESR_ELx_EC_HVC32 || esr_ec == ESR_ELx_EC_HVC64)
+			*vcpu_pc(vcpu) -= 4;
 
 		return 1;
 	}