[PATCH v2 2/6] KVM: arm64: Guard against NULL vcpu on VHE hyp panic path

[Fuad Tabba <tabba@google.com>]

On VHE, __hyp_call_panic() unconditionally calls __deactivate_traps(vcpu)
on the vcpu pointer read from host_ctxt->__hyp_running_vcpu. That pointer
is cleared after every guest exit (and is never set when no guest is
running), so an unexpected EL2 exception landing in _guest_exit_panic,
e.g. via the el2t*_invalid / el2h_irq_invalid vectors - reaches this
function with vcpu == NULL. __deactivate_traps() then dereferences vcpu
via ___deactivate_traps() -> vserror_state_is_nested() -> vcpu_has_nv()
-> vcpu->arch.features, faulting inside the panic handler and obscuring
the original failure.

The nVHE counterpart (hyp_panic() in arch/arm64/kvm/hyp/nvhe/switch.c)
already guards its vcpu-using cleanup with "if (vcpu)"; mirror that
here. sysreg_restore_host_state_vhe() does not depend on vcpu and
continues to run unconditionally, preserving panic forensics. The
trailing panic("...VCPU:%p", vcpu) prints "(null)" safely via printk's
%p handling.

Fixes: 6a0259ed29bb ("KVM: arm64: Remove hyp_panic arguments")
Assisted-by: Gemini:gemini-3.1-pro review-prompts
Signed-off-by: Fuad Tabba <tabba@google.com>
---
 arch/arm64/kvm/hyp/vhe/switch.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index 9db3f11a4754..1e8995add14f 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -663,7 +663,8 @@ static void __noreturn __hyp_call_panic(u64 spsr, u64 elr, u64 par)
 	host_ctxt = host_data_ptr(host_ctxt);
 	vcpu = host_ctxt->__hyp_running_vcpu;
 
-	__deactivate_traps(vcpu);
+	if (vcpu)
+		__deactivate_traps(vcpu);
 	sysreg_restore_host_state_vhe(host_ctxt);
 
 	panic("HYP panic:\nPS:%08llx PC:%016llx ESR:%08llx\nFAR:%016llx HPFAR:%016llx PAR:%016llx\nVCPU:%p\n",
-- 
2.54.0.545.g6539524ca2-goog