[PATCH v3 7/8] KVM: kvm-vfio: generic forwarding control

[Eric Auger]

This patch introduces a new KVM_DEV_VFIO_DEVICE group.

This is a new control channel which enables KVM to cooperate with
viable VFIO devices.

Functions are introduced to check the validity of a VFIO device
file descriptor, increment/decrement the ref counter of the VFIO
device.

The patch introduces 2 attributes for this new device group:
KVM_DEV_VFIO_DEVICE_FORWARD_IRQ, KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ.
Their purpose is to turn a VFIO device IRQ into a forwarded IRQ and
unset respectively unset the feature.

The VFIO device stores a list of registered forwarded IRQs. The reference
counter of the device is incremented each time a new IRQ is forwarded.
Reference counter is decremented when the IRQ forwarding is unset.

The forwarding programmming is architecture specific, implemented in
kvm_arch_set_fwd_state function. Architecture specific implementation is
enabled when __KVM_HAVE_ARCH_KVM_VFIO_FORWARD is set. When not set those
functions are void.

Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>

---

v2 -> v3:
- add API comments in kvm_host.h
- improve the commit message
- create a private kvm_vfio_fwd_irq struct
- fwd_irq_action replaced by a bool and removal of VFIO_IRQ_CLEANUP. This
  latter action will be handled in vgic.
- add a vfio_device handle argument to kvm_arch_set_fwd_state. The goal is
  to move platform specific stuff in architecture specific code.
- kvm_arch_set_fwd_state renamed into kvm_arch_vfio_set_forward
- increment the ref counter each time we do an IRQ forwarding and decrement
  this latter each time one IRQ forward is unset. Simplifies the whole
  ref counting.
- simplification of list handling: create, search, removal

v1 -> v2:
- __KVM_HAVE_ARCH_KVM_VFIO renamed into __KVM_HAVE_ARCH_KVM_VFIO_FORWARD
- original patch file separated into 2 parts: generic part moved in vfio.c
  and ARM specific part(kvm_arch_set_fwd_state)
---
 include/linux/kvm_host.h |  28 ++++++
 virt/kvm/vfio.c          | 249 ++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 274 insertions(+), 3 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ea53b04..0b9659d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1076,6 +1076,15 @@ struct kvm_device_ops {
 		      unsigned long arg);
 };
 
+/* internal self-contained structure describing a forwarded IRQ */
+struct kvm_fwd_irq {
+	struct kvm *kvm; /* VM to inject the GSI into */
+	struct vfio_device *vdev; /* vfio device the IRQ belongs to */
+	__u32 index; /* VFIO device IRQ index */
+	__u32 subindex; /* VFIO device IRQ subindex */
+	__u32 gsi; /* gsi, ie. virtual IRQ number */
+};
+
 void kvm_device_get(struct kvm_device *dev);
 void kvm_device_put(struct kvm_device *dev);
 struct kvm_device *kvm_device_from_filp(struct file *filp);
@@ -1085,6 +1094,25 @@ void kvm_unregister_device_ops(u32 type);
 extern struct kvm_device_ops kvm_mpic_ops;
 extern struct kvm_device_ops kvm_xics_ops;
 
+#ifdef __KVM_HAVE_ARCH_KVM_VFIO_FORWARD
+/**
+ * kvm_arch_vfio_set_forward - changes the forwarded state of an IRQ
+ *
+ * @fwd_irq: handle to the forwarded irq struct
+ * @forward: true means forwarded, false means not forwarded
+ * returns 0 on success, < 0 on failure
+ */
+int kvm_arch_vfio_set_forward(struct kvm_fwd_irq *fwd_irq,
+			      bool forward);
+
+#else
+static inline int kvm_arch_vfio_set_forward(struct kvm_fwd_irq *fwd_irq,
+					    bool forward)
+{
+	return 0;
+}
+#endif
+
 #ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT
 
 static inline void kvm_vcpu_set_in_spin_loop(struct kvm_vcpu *vcpu, bool val)
diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
index 6f0cc34..af178bb 100644
--- a/virt/kvm/vfio.c
+++ b/virt/kvm/vfio.c
@@ -25,8 +25,16 @@ struct kvm_vfio_group {
 	struct vfio_group *vfio_group;
 };
 
+/* private linkable kvm_fwd_irq struct */
+struct kvm_vfio_fwd_irq_node {
+	struct list_head link;
+	struct kvm_fwd_irq fwd_irq;
+};
+
 struct kvm_vfio {
 	struct list_head group_list;
+	/* list of registered VFIO forwarded IRQs */
+	struct list_head fwd_node_list;
 	struct mutex lock;
 	bool noncoherent;
 };
@@ -247,12 +255,239 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
 	return -ENXIO;
 }
 
+/**
+ * kvm_vfio_get_vfio_device - Returns a handle to a vfio-device
+ *
+ * Checks it is a valid vfio device and increments its reference counter
+ * @fd: file descriptor of the vfio platform device
+ */
+static struct vfio_device *kvm_vfio_get_vfio_device(int fd)
+{
+	struct fd f = fdget(fd);
+	struct vfio_device *vdev;
+
+	if (!f.file)
+		return NULL;
+	vdev = kvm_vfio_device_get_external_user(f.file);
+	fdput(f);
+	return vdev;
+}
+
+/**
+ * kvm_vfio_put_vfio_device: decrements the reference counter of the
+ * vfio platform * device
+ *
+ * @vdev: vfio_device handle to release
+ */
+static void kvm_vfio_put_vfio_device(struct vfio_device *vdev)
+{
+	kvm_vfio_device_put_external_user(vdev);
+}
+
+/**
+ * kvm_vfio_find_fwd_irq - checks whether a forwarded IRQ already is
+ * registered in the list of forwarded IRQs
+ *
+ * @kv: handle to the kvm-vfio device
+ * @fwd: handle to the forwarded irq struct
+ * In the positive returns the handle to its node in the kvm-vfio
+ * forwarded IRQ list, returns NULL otherwise.
+ * Must be called with kv->lock hold.
+ */
+static struct kvm_vfio_fwd_irq_node *kvm_vfio_find_fwd_irq(
+				struct kvm_vfio *kv,
+				struct kvm_fwd_irq *fwd)
+{
+	struct kvm_vfio_fwd_irq_node *node;
+
+	list_for_each_entry(node, &kv->fwd_node_list, link) {
+		if ((node->fwd_irq.index == fwd->index) &&
+		    (node->fwd_irq.subindex == fwd->subindex) &&
+		    (node->fwd_irq.vdev == fwd->vdev))
+			return node;
+	}
+	return NULL;
+}
+/**
+ * kvm_vfio_register_fwd_irq - Allocates, populates and registers a
+ * forwarded IRQ
+ *
+ * @kv: handle to the kvm-vfio device
+ * @fwd: handle to the forwarded irq struct
+ * In case of success returns a handle to the new list node,
+ * NULL otherwise.
+ * Must be called with kv->lock hold.
+ */
+static struct kvm_vfio_fwd_irq_node *kvm_vfio_register_fwd_irq(
+				struct kvm_vfio *kv,
+				struct kvm_fwd_irq *fwd)
+{
+	struct kvm_vfio_fwd_irq_node *node;
+
+	node = kmalloc(sizeof(*node), GFP_KERNEL);
+	if (!node)
+		return NULL;
+
+	node->fwd_irq = *fwd;
+
+	list_add(&node->link, &kv->fwd_node_list);
+
+	return node;
+}
+
+/**
+ * kvm_vfio_unregister_fwd_irq - unregisters and frees a forwarded IRQ
+ *
+ * @node: handle to the node struct
+ * Must be called with kv->lock hold.
+ */
+static void kvm_vfio_unregister_fwd_irq(struct kvm_vfio_fwd_irq_node *node)
+{
+	list_del(&node->link);
+	kfree(node);
+}
+
+/**
+ * kvm_vfio_set_forward - turns a VFIO device IRQ into a forwarded IRQ
+ * @kv: handle to the kvm-vfio device
+ * @fd: file descriptor of the vfio device the IRQ belongs to
+ * @fwd: handle to the forwarded irq struct
+ *
+ * Registers an IRQ as forwarded and calls the architecture specific
+ * implementation of set_forward. In case of operation failure, the IRQ
+ * is unregistered. In case of success, the vfio device ref counter is
+ * incremented.
+ */
+static int kvm_vfio_set_forward(struct kvm_vfio *kv, int fd,
+				struct kvm_fwd_irq *fwd)
+{
+	int ret;
+	struct kvm_vfio_fwd_irq_node *node =
+			kvm_vfio_find_fwd_irq(kv, fwd);
+
+	if (node)
+		return -EINVAL;
+	node = kvm_vfio_register_fwd_irq(kv, fwd);
+	if (!node)
+		return -ENOMEM;
+	ret = kvm_arch_vfio_set_forward(fwd, true);
+	if (ret < 0)  {
+		kvm_vfio_unregister_fwd_irq(node);
+		return ret;
+	}
+	/* increment the ref counter */
+	kvm_vfio_get_vfio_device(fd);
+	return ret;
+}
+
+/**
+ * kvm_vfio_unset_forward - Sets a VFIO device IRQ as non forwarded
+ * @kv: handle to the kvm-vfio device
+ * @fwd: handle to the forwarded irq struct
+ *
+ * Calls the architecture specific implementation of set_forward and
+ * unregisters the IRQ from the forwarded IRQ list. Decrements the vfio
+ * device reference counter.
+ */
+static int kvm_vfio_unset_forward(struct kvm_vfio *kv,
+				  struct kvm_fwd_irq *fwd)
+{
+	int ret;
+	struct kvm_vfio_fwd_irq_node *node =
+			kvm_vfio_find_fwd_irq(kv, fwd);
+	if (!node)
+		return -EINVAL;
+	ret = kvm_arch_vfio_set_forward(fwd, false);
+	kvm_vfio_unregister_fwd_irq(node);
+
+	/* decrement the ref counter */
+	kvm_vfio_put_vfio_device(fwd->vdev);
+	return ret;
+}
+
+static int kvm_vfio_control_irq_forward(struct kvm_device *kdev, long attr,
+					int32_t __user *argp)
+{
+	struct kvm_arch_forwarded_irq user_fwd_irq;
+	struct kvm_fwd_irq fwd;
+	struct vfio_device *vdev;
+	struct kvm_vfio *kv = kdev->private;
+	int ret;
+
+	if (copy_from_user(&user_fwd_irq, argp, sizeof(user_fwd_irq)))
+		return -EFAULT;
+
+	vdev = kvm_vfio_get_vfio_device(user_fwd_irq.fd);
+	if (IS_ERR(vdev)) {
+		ret = PTR_ERR(vdev);
+		goto out;
+	}
+
+	fwd.vdev =  vdev;
+	fwd.kvm =  kdev->kvm;
+	fwd.index = user_fwd_irq.index;
+	fwd.subindex = user_fwd_irq.subindex;
+	fwd.gsi = user_fwd_irq.gsi;
+
+	switch (attr) {
+	case KVM_DEV_VFIO_DEVICE_FORWARD_IRQ:
+		mutex_lock(&kv->lock);
+		ret = kvm_vfio_set_forward(kv, user_fwd_irq.fd, &fwd);
+		mutex_unlock(&kv->lock);
+		break;
+	case KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ:
+		mutex_lock(&kv->lock);
+		ret = kvm_vfio_unset_forward(kv, &fwd);
+		mutex_unlock(&kv->lock);
+		break;
+	}
+out:
+	kvm_vfio_put_vfio_device(vdev);
+	return ret;
+}
+
+static int kvm_vfio_set_device(struct kvm_device *kdev, long attr, u64 arg)
+{
+	int32_t __user *argp = (int32_t __user *)(unsigned long)arg;
+	int ret;
+
+	switch (attr) {
+	case KVM_DEV_VFIO_DEVICE_FORWARD_IRQ:
+	case KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ:
+		ret = kvm_vfio_control_irq_forward(kdev, attr, argp);
+		break;
+	default:
+		ret = -ENXIO;
+	}
+	return ret;
+}
+
+/**
+ * kvm_vfio_clean_fwd_irq - Unset forwarding state of all
+ * registered forwarded IRQs and free their list nodes.
+ * @kv: kvm-vfio device
+ *
+ * Loop on all registered device/IRQ combos, reset the non forwarded state,
+ * void the lists and release the reference
+ */
+static int kvm_vfio_clean_fwd_irq(struct kvm_vfio *kv)
+{
+	struct kvm_vfio_fwd_irq_node *node, *tmp;
+
+	list_for_each_entry_safe(node, tmp, &kv->fwd_node_list, link) {
+		kvm_vfio_unset_forward(kv, &node->fwd_irq);
+	}
+	return 0;
+}
+
 static int kvm_vfio_set_attr(struct kvm_device *dev,
 			     struct kvm_device_attr *attr)
 {
 	switch (attr->group) {
 	case KVM_DEV_VFIO_GROUP:
 		return kvm_vfio_set_group(dev, attr->attr, attr->addr);
+	case KVM_DEV_VFIO_DEVICE:
+		return kvm_vfio_set_device(dev, attr->attr, attr->addr);
 	}
 
 	return -ENXIO;
@@ -268,10 +503,17 @@ static int kvm_vfio_has_attr(struct kvm_device *dev,
 		case KVM_DEV_VFIO_GROUP_DEL:
 			return 0;
 		}
-
 		break;
+#ifdef __KVM_HAVE_ARCH_KVM_VFIO_FORWARD
+	case KVM_DEV_VFIO_DEVICE:
+		switch (attr->attr) {
+		case KVM_DEV_VFIO_DEVICE_FORWARD_IRQ:
+		case KVM_DEV_VFIO_DEVICE_UNFORWARD_IRQ:
+			return 0;
+		}
+		break;
+#endif
 	}
-
 	return -ENXIO;
 }
 
@@ -285,7 +527,7 @@ static void kvm_vfio_destroy(struct kvm_device *dev)
 		list_del(&kvg->node);
 		kfree(kvg);
 	}
-
+	kvm_vfio_clean_fwd_irq(kv);
 	kvm_vfio_update_coherency(dev);
 
 	kfree(kv);
@@ -317,6 +559,7 @@ static int kvm_vfio_create(struct kvm_device *dev, u32 type)
 		return -ENOMEM;
 
 	INIT_LIST_HEAD(&kv->group_list);
+	INIT_LIST_HEAD(&kv->fwd_node_list);
 	mutex_init(&kv->lock);
 
 	dev->private = kv;
-- 
1.9.1

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