KVM: arm: Fix DFSR setting for non-LPAE aarch32 guests

Beata reports that KVM_SET_VCPU_EVENTS doesn't inject the expected
exception to a non-LPAE aarch32 guest.

The host intends to inject DFSR.FS=0x14 "IMPLEMENTATION DEFINED fault
(Lockdown fault)", but the guest receives DFSR.FS=0x04 "Fault on
instruction cache maintenance". This fault is hooked by
do_translation_fault() since ARMv6, which goes on to silently 'handle'
the exception, and restart the faulting instruction.

It turns out, when TTBCR.EAE is clear DFSR is split, and FS[4] has
to shuffle up to DFSR[10].

As KVM only does this in one place, fix up the static values. We
now get the expected:
| Unhandled fault: lock abort (0x404) at 0x9c800f00

Fixes: 74a64a9 ("KVM: arm/arm64: Unify 32bit fault injection")
Reported-by: Beata Michalska <[email protected]>
Signed-off-by: James Morse <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: James Morse

virt/kvm/arm/aarch32.c

@@ -181,10 +181,12 @@ 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)
+	if (is_lpae) {
 		*fsr = 1 << 9 | 0x34;
-	else
-		*fsr = 0x14;
+	} else {
+		/* Surprise! DFSR's FS[4] lives in bit 10 */
+		*fsr = BIT(10) | 0x4; /* 0x14 */
+	}
 }
 
 void kvm_inject_dabt32(struct kvm_vcpu *vcpu, unsigned long addr)