KVM: arm64: Separate out feature sanitisation and initialisation

kvm_vcpu_set_target() iteratively sanitises and copies feature flags in
one go. This is rather odd, especially considering the fact that bitmap
accessors can do the heavy lifting. A subsequent change will make vCPU
features VM-wide, and fitting that into the present implementation is
just a chore.

Rework the whole thing to use bitmap accessors to sanitise and copy
flags.

Link: https://lore.kernel.org/r/20230609190054.1542113-2-oliver.upton@linux.devSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_host.h

@@ -39,6 +39,7 @@
 #define KVM_MAX_VCPUS VGIC_V3_MAX_CPUS
 
 #define KVM_VCPU_MAX_FEATURES 7
+#define KVM_VCPU_VALID_FEATURES	(BIT(KVM_VCPU_MAX_FEATURES) - 1)
 
 #define KVM_REQ_SLEEP \
 	KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)

arch/arm64/kvm/arm.c

@@ -1167,42 +1167,40 @@ 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,
+static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu,
 					const struct kvm_vcpu_init *init)
 {
-	unsigned int i, ret;
-	u32 phys_target = kvm_target_cpu();
+	unsigned long features = init->features[0];
+	int i;
 
-	if (init->target != phys_target)
-		return -EINVAL;
+	if (features & ~KVM_VCPU_VALID_FEATURES)
+		return -ENOENT;
 
-	/*
-	 * 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;
+	for (i = 1; i < ARRAY_SIZE(init->features); i++) {
+		if (init->features[i])
+			return -ENOENT;
+	}
 
-	/* -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)));
+	return 0;
+}
 
-		if (set && i >= KVM_VCPU_MAX_FEATURES)
-			return -ENOENT;
+static bool kvm_vcpu_init_changed(struct kvm_vcpu *vcpu,
+				  const struct kvm_vcpu_init *init)
+{
+	unsigned long features = init->features[0];
 
-		/*
-		 * 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;
+	return !bitmap_equal(vcpu->arch.features, &features, KVM_VCPU_MAX_FEATURES) ||
+			vcpu->arch.target != init->target;
+}
 
-		if (set)
-			set_bit(i, vcpu->arch.features);
-	}
+static int __kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
+				 const struct kvm_vcpu_init *init)
+{
+	unsigned long features = init->features[0];
+	int ret;
 
-	vcpu->arch.target = phys_target;
+	vcpu->arch.target = init->target;
+	bitmap_copy(vcpu->arch.features, &features, KVM_VCPU_MAX_FEATURES);
 
 	/* Now we know what it is, we can reset it. */
 	ret = kvm_reset_vcpu(vcpu);
@@ -1214,6 +1212,27 @@ static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
 	return ret;
 }
 
+static int kvm_vcpu_set_target(struct kvm_vcpu *vcpu,
+			       const struct kvm_vcpu_init *init)
+{
+	int ret;
+
+	if (init->target != kvm_target_cpu())
+		return -EINVAL;
+
+	ret = kvm_vcpu_init_check_features(vcpu, init);
+	if (ret)
+		return ret;
+
+	if (vcpu->arch.target == -1)
+		return __kvm_vcpu_set_target(vcpu, init);
+
+	if (kvm_vcpu_init_changed(vcpu, init))
+		return -EINVAL;
+
+	return kvm_reset_vcpu(vcpu);
+}
+
 static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,
 					 struct kvm_vcpu_init *init)
 {