KVM: arm: Make inject_abt32() inject an external abort instead

KVM's inject_abt64() injects an external-abort into an aarch64 guest.
The KVM_CAP_ARM_INJECT_EXT_DABT is intended to do exactly this, but
for an aarch32 guest inject_abt32() injects an implementation-defined
exception, 'Lockdown fault'.

Change this to external abort. For non-LPAE we now get the documented:
| Unhandled fault: external abort on non-linefetch (0x008) at 0x9c800f00
and for LPAE:
| Unhandled fault: synchronous external abort (0x210) at 0x9c800f00

Fixes: 74a64a98 ("KVM: arm/arm64: Unify 32bit fault injection")
Reported-by: Beata Michalska <beata.michalska@linaro.org>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200121123356.203000-3-james.morse@arm.com

virt/kvm/arm/aarch32.c

@@ -15,6 +15,10 @@
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_hyp.h>
 
+#define DFSR_FSC_EXTABT_LPAE	0x10
+#define DFSR_FSC_EXTABT_nLPAE	0x08
+#define DFSR_LPAE		BIT(9)
+
 /*
  * Table taken from ARMv8 ARM DDI0487B-B, table G1-10.
  */
@@ -182,10 +186,10 @@ static void inject_abt32(struct kvm_vcpu *vcpu, bool is_pabt,
 	/* Give the guest an IMPLEMENTATION DEFINED exception */
 	is_lpae = (vcpu_cp15(vcpu, c2_TTBCR) >> 31);
 	if (is_lpae) {
-		*fsr = 1 << 9 | 0x34;
+		*fsr = DFSR_LPAE | DFSR_FSC_EXTABT_LPAE;
 	} else {
-		/* Surprise! DFSR's FS[4] lives in bit 10 */
-		*fsr = BIT(10) | 0x4; /* 0x14 */
+		/* no need to shuffle FS[4] into DFSR[10] as its 0 */
+		*fsr = DFSR_FSC_EXTABT_nLPAE;
 	}
 }