KVM: arm64: Fully zero the vcpu state on reset

On vcpu reset, we expect all the registers to be brought back
to their initial state, which happens to be a bunch of zeroes.

However, some recent commit broke this, and is now leaving a bunch
of registers (such as the FP state) with whatever was left by the
guest. My bad.

Zero the reset of the state (32bit SPSRs and FPSIMD state).

Cc: stable@vger.kernel.org
Fixes: e47c2055 ("KVM: arm64: Make struct kvm_regs userspace-only")
Signed-off-by: NMarc Zyngier <maz@kernel.org>

arch/arm64/kvm/reset.c

@@ -242,6 +242,11 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 
 	/* Reset core registers */
 	memset(vcpu_gp_regs(vcpu), 0, sizeof(*vcpu_gp_regs(vcpu)));
+	memset(&vcpu->arch.ctxt.fp_regs, 0, sizeof(vcpu->arch.ctxt.fp_regs));
+	vcpu->arch.ctxt.spsr_abt = 0;
+	vcpu->arch.ctxt.spsr_und = 0;
+	vcpu->arch.ctxt.spsr_irq = 0;
+	vcpu->arch.ctxt.spsr_fiq = 0;
 	vcpu_gp_regs(vcpu)->pstate = pstate;
 
 	/* Reset system registers */