[PATCH] ARM: KVM: Emulate ID_DFR0 to say we don't support anything.

["Rusty Russell" <rusty.russell@linaro.org>]

The guest should be checking this before trying to use performance monitors,
for example.

Signed-off-by: Rusty Russell <rusty.russell@linaro.org>

diff --git a/arch/arm/kvm/emulate.c b/arch/arm/kvm/emulate.c
index e356d1c..c07eb2b 100644
--- a/arch/arm/kvm/emulate.c
+++ b/arch/arm/kvm/emulate.c
@@ -238,6 +238,15 @@ static bool read_l2ctlr(struct kvm_vcpu *vcpu,
 	return true;
 }
 
+static bool read_id_dfr0(struct kvm_vcpu *vcpu,
+			 const struct coproc_params *p,
+			 unsigned long arg)
+{
+	/* We support no performance monitors (27-24 = b1111) and no debug */
+	*vcpu_reg(vcpu, p->Rt1) = 0x0F000000;
+	return true;
+}
+
 static bool access_cp15_reg(struct kvm_vcpu *vcpu,
 			    const struct coproc_params *p,
 			    unsigned long cp15_reg)
@@ -277,6 +286,9 @@ struct coproc_emulate {
 #define RW		.is_w  = DF
 
 static const struct coproc_emulate coproc_emulate[] = {
+	/* ID_DFR0 (guest asks what PMU/debug we support) */
+	{ CRn( 0), CRm( 1), Op1( 0), Op2( 2), is32,  READ,  read_id_dfr0},
+
 	/*
 	 * L2CTLR access:
 	 *