[PATCH 17/23] KVM: arm: Fix DFSR setting for non-LPAE aarch32 guests

Marc Zyngier
2020-01-30T13:29:20Z

From: James Morse <james.morse@arm.com>

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: 74a64a981662a ("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/20200121123356.203000-2-james.morse@arm.com
---
virt/kvm/arm/aarch32.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/arm/aarch32.c b/virt/kvm/arm/aarch32.c
index 631d397ac81b..2da482ca7067 100644
--- a/virt/kvm/arm/aarch32.c
+++ b/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)
--
2.20.1