arm/arm64: KVM: Clarify KVM_ARM_VCPU_INIT ABI

It is not clear that this ioctl can be called multiple times for a given
vcpu.  Userspace already does this, so clarify the ABI.

Also specify that userspace is expected to always make secondary and
subsequent calls to the ioctl with the same parameters for the VCPU as
the initial call (which userspace also already does).

Add code to check that userspace doesn't violate that ABI in the future,
and move the kvm_vcpu_set_target() function which is currently
duplicated between the 32-bit and 64-bit versions in guest.c to a common
static function in arm.c, shared between both architectures.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

3 files changed, 43 insertions, 27 deletions

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 53036e21756..254e0650e48 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -150,8 +150,6 @@ struct kvm_vcpu_stat {
 	u32 halt_wakeup;
 };
 
-int kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
-			const struct kvm_vcpu_init *init);
 int kvm_vcpu_preferred_target(struct kvm_vcpu_init *init);
 unsigned long kvm_arm_num_regs(struct kvm_vcpu *vcpu);
 int kvm_arm_copy_reg_indices(struct kvm_vcpu *vcpu, u64 __user *indices);
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 24c9ca4076b..4043769583e 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -263,6 +263,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 {
 	/* Force users to call KVM_ARM_VCPU_INIT */
 	vcpu->arch.target = -1;
+	bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES);
 
 	/* Set up the timer */
 	kvm_timer_vcpu_init(vcpu);
@@ -649,6 +650,48 @@ int kvm_vm_ioctl_irq_line(struct kvm *kvm, struct kvm_irq_level *irq_level,
 	return -EINVAL;
 }
 
+static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
+			       const struct kvm_vcpu_init *init)
+{
+	unsigned int i;
+	int phys_target = kvm_target_cpu();
+
+	if (init->target != phys_target)
+		return -EINVAL;
+
+	/*
+	 * Secondary and subsequent calls to KVM_ARM_VCPU_INIT must
+	 * use the same target.
+	 */
+	if (vcpu->arch.target != -1 && vcpu->arch.target != init->target)
+		return -EINVAL;
+
+	/* -ENOENT for unknown features, -EINVAL for invalid combinations. */
+	for (i = 0; i < sizeof(init->features) * 8; i++) {
+		bool set = (init->features[i / 32] & (1 << (i % 32)));
+
+		if (set && i >= KVM_VCPU_MAX_FEATURES)
+			return -ENOENT;
+
+		/*
+		 * Secondary and subsequent calls to KVM_ARM_VCPU_INIT must
+		 * use the same feature set.
+		 */
+		if (vcpu->arch.target != -1 && i < KVM_VCPU_MAX_FEATURES &&
+		    test_bit(i, vcpu->arch.features) != set)
+			return -EINVAL;
+
+		if (set)
+			set_bit(i, vcpu->arch.features);
+	}
+
+	vcpu->arch.target = phys_target;
+
+	/* Now we know what it is, we can reset it. */
+	return kvm_reset_vcpu(vcpu);
+}
+
+
 static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,
 					 struct kvm_vcpu_init *init)
 {
diff --git a/arch/arm/kvm/guest.c b/arch/arm/kvm/guest.c
index 8c97208b9b9..384bab67c46 100644
--- a/arch/arm/kvm/guest.c
+++ b/arch/arm/kvm/guest.c
@@ -273,31 +273,6 @@ int __attribute_const__ kvm_target_cpu(void)
 	}
 }
 
-int kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
-			const struct kvm_vcpu_init *init)
-{
-	unsigned int i;
-
-	/* We can only cope with guest==host and only on A15/A7 (for now). */
-	if (init->target != kvm_target_cpu())
-		return -EINVAL;
-
-	vcpu->arch.target = init->target;
-	bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES);
-
-	/* -ENOENT for unknown features, -EINVAL for invalid combinations. */
-	for (i = 0; i < sizeof(init->features) * 8; i++) {
-		if (test_bit(i, (void *)init->features)) {
-			if (i >= KVM_VCPU_MAX_FEATURES)
-				return -ENOENT;
-			set_bit(i, vcpu->arch.features);
-		}
-	}
-
-	/* Now we know what it is, we can reset it. */
-	return kvm_reset_vcpu(vcpu);
-}
-
 int kvm_vcpu_preferred_target(struct kvm_vcpu_init *init)
 {
 	int target = kvm_target_cpu();