MIPS: KVM: Make KVM_GET_REG_LIST dynamic

Make the implementation of KVM_GET_REG_LIST more dynamic so that only
the subset of registers actually available can be exposed to user mode.
This is important for VZ where some of the guest register state may not
be possible to prevent the guest from accessing, therefore the user
process may need to be aware of the state even if it doesn't understand
what the state is for.

This also allows different MIPS KVM implementations to provide different
registers to one another, by way of new num_regs(vcpu) and
copy_reg_indices(vcpu, indices) callback functions, currently just
stubbed for trap & emulate.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/mips/include/asm/kvm_host.h

@@ -560,6 +560,8 @@ struct kvm_mips_callbacks {
 			   u32 cause);
 	int (*irq_clear)(struct kvm_vcpu *vcpu, unsigned int priority,
 			 u32 cause);
+	unsigned long (*num_regs)(struct kvm_vcpu *vcpu);
+	int (*copy_reg_indices)(struct kvm_vcpu *vcpu, u64 __user *indices);
 	int (*get_one_reg)(struct kvm_vcpu *vcpu,
 			   const struct kvm_one_reg *reg, s64 *v);
 	int (*set_one_reg)(struct kvm_vcpu *vcpu,

arch/mips/kvm/mips.c

@@ -538,6 +538,26 @@ static u64 kvm_mips_get_one_regs[] = {
 	KVM_REG_MIPS_COUNT_HZ,
 };
 
+static unsigned long kvm_mips_num_regs(struct kvm_vcpu *vcpu)
+{
+	unsigned long ret;
+
+	ret = ARRAY_SIZE(kvm_mips_get_one_regs);
+	ret += kvm_mips_callbacks->num_regs(vcpu);
+
+	return ret;
+}
+
+static int kvm_mips_copy_reg_indices(struct kvm_vcpu *vcpu, u64 __user *indices)
+{
+	if (copy_to_user(indices, kvm_mips_get_one_regs,
+			 sizeof(kvm_mips_get_one_regs)))
+		return -EFAULT;
+	indices += ARRAY_SIZE(kvm_mips_get_one_regs);
+
+	return kvm_mips_callbacks->copy_reg_indices(vcpu, indices);
+}
+
 static int kvm_mips_get_reg(struct kvm_vcpu *vcpu,
 			    const struct kvm_one_reg *reg)
 {
@@ -908,23 +928,18 @@ long kvm_arch_vcpu_ioctl(struct file *filp, unsigned int ioctl,
 	}
 	case KVM_GET_REG_LIST: {
 		struct kvm_reg_list __user *user_list = argp;
-		u64 __user *reg_dest;
 		struct kvm_reg_list reg_list;
 		unsigned n;
 
 		if (copy_from_user(&reg_list, user_list, sizeof(reg_list)))
 			return -EFAULT;
 		n = reg_list.n;
-		reg_list.n = ARRAY_SIZE(kvm_mips_get_one_regs);
+		reg_list.n = kvm_mips_num_regs(vcpu);
 		if (copy_to_user(user_list, &reg_list, sizeof(reg_list)))
 			return -EFAULT;
 		if (n < reg_list.n)
 			return -E2BIG;
-		reg_dest = user_list->reg;
-		if (copy_to_user(reg_dest, kvm_mips_get_one_regs,
-				 sizeof(kvm_mips_get_one_regs)))
-			return -EFAULT;
-		return 0;
+		return kvm_mips_copy_reg_indices(vcpu, user_list->reg);
 	}
 	case KVM_NMI:
 		/* Treat the NMI as a CPU reset */

arch/mips/kvm/trap_emul.c

@@ -478,6 +478,17 @@ static int kvm_trap_emul_vcpu_setup(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+static unsigned long kvm_trap_emul_num_regs(struct kvm_vcpu *vcpu)
+{
+	return 0;
+}
+
+static int kvm_trap_emul_copy_reg_indices(struct kvm_vcpu *vcpu,
+					  u64 __user *indices)
+{
+	return 0;
+}
+
 static int kvm_trap_emul_get_one_reg(struct kvm_vcpu *vcpu,
 				     const struct kvm_one_reg *reg,
 				     s64 *v)
@@ -627,6 +638,8 @@ static struct kvm_mips_callbacks kvm_trap_emul_callbacks = {
 	.dequeue_io_int = kvm_mips_dequeue_io_int_cb,
 	.irq_deliver = kvm_mips_irq_deliver_cb,
 	.irq_clear = kvm_mips_irq_clear_cb,
+	.num_regs = kvm_trap_emul_num_regs,
+	.copy_reg_indices = kvm_trap_emul_copy_reg_indices,
 	.get_one_reg = kvm_trap_emul_get_one_reg,
 	.set_one_reg = kvm_trap_emul_set_one_reg,
 	.vcpu_get_regs = kvm_trap_emul_vcpu_get_regs,