kvm: Add VFIO device

So far we've succeeded at making KVM and VFIO mostly unaware of each
other, but areas are cropping up where a connection beyond eventfds
and irqfds needs to be made.  This patch introduces a KVM-VFIO device
that is meant to be a gateway for such interaction.  The user creates
the device and can add and remove VFIO groups to it via file
descriptors.  When a group is added, KVM verifies the group is valid
and gets a reference to it via the VFIO external user interface.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 228 insertions, 0 deletions

diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 779262f59e25..fbe1a48bd629 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -27,3 +27,6 @@ config HAVE_KVM_MSI
 
 config HAVE_KVM_CPU_RELAX_INTERCEPT
        bool
+
+config KVM_VFIO
+       bool
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 9ca014da134d..82c4047aa0e3 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2271,6 +2271,11 @@ static int kvm_ioctl_create_device(struct kvm *kvm,
                 ops = &kvm_xics_ops;
                 break;
 #endif
+#ifdef CONFIG_KVM_VFIO
+        case KVM_DEV_TYPE_VFIO:
+                ops = &kvm_vfio_ops;
+                break;
+#endif
         default:
                 return -ENODEV;
         }
diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
new file mode 100644
index 000000000000..597c258245ea
--- /dev/null
+++ b/virt/kvm/vfio.c
@@ -0,0 +1,220 @@
+/*
+ * VFIO-KVM bridge pseudo device
+ *
+ * Copyright (C) 2013 Red Hat, Inc.  All rights reserved.
+ *     Author: Alex Williamson <alex.williamson@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/errno.h>
+#include <linux/file.h>
+#include <linux/kvm_host.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/vfio.h>
+
+struct kvm_vfio_group {
+        struct list_head node;
+        struct vfio_group *vfio_group;
+};
+
+struct kvm_vfio {
+        struct list_head group_list;
+        struct mutex lock;
+};
+
+static struct vfio_group *kvm_vfio_group_get_external_user(struct file *filep)
+{
+        struct vfio_group *vfio_group;
+        struct vfio_group *(*fn)(struct file *);
+
+        fn = symbol_get(vfio_group_get_external_user);
+        if (!fn)
+                return ERR_PTR(-EINVAL);
+
+        vfio_group = fn(filep);
+
+        symbol_put(vfio_group_get_external_user);
+
+        return vfio_group;
+}
+
+static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
+{
+        void (*fn)(struct vfio_group *);
+
+        fn = symbol_get(vfio_group_put_external_user);
+        if (!fn)
+                return;
+
+        fn(vfio_group);
+
+        symbol_put(vfio_group_put_external_user);
+}
+
+static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
+{
+        struct kvm_vfio *kv = dev->private;
+        struct vfio_group *vfio_group;
+        struct kvm_vfio_group *kvg;
+        void __user *argp = (void __user *)arg;
+        struct fd f;
+        int32_t fd;
+        int ret;
+
+        switch (attr) {
+        case KVM_DEV_VFIO_GROUP_ADD:
+                if (get_user(fd, (int32_t __user *)argp))
+                        return -EFAULT;
+
+                f = fdget(fd);
+                if (!f.file)
+                        return -EBADF;
+
+                vfio_group = kvm_vfio_group_get_external_user(f.file);
+                fdput(f);
+
+                if (IS_ERR(vfio_group))
+                        return PTR_ERR(vfio_group);
+
+                mutex_lock(&kv->lock);
+
+                list_for_each_entry(kvg, &kv->group_list, node) {
+                        if (kvg->vfio_group == vfio_group) {
+                                mutex_unlock(&kv->lock);
+                                kvm_vfio_group_put_external_user(vfio_group);
+                                return -EEXIST;
+                        }
+                }
+
+                kvg = kzalloc(sizeof(*kvg), GFP_KERNEL);
+                if (!kvg) {
+                        mutex_unlock(&kv->lock);
+                        kvm_vfio_group_put_external_user(vfio_group);
+                        return -ENOMEM;
+                }
+
+                list_add_tail(&kvg->node, &kv->group_list);
+                kvg->vfio_group = vfio_group;
+
+                mutex_unlock(&kv->lock);
+
+                return 0;
+
+        case KVM_DEV_VFIO_GROUP_DEL:
+                if (get_user(fd, (int32_t __user *)argp))
+                        return -EFAULT;
+
+                f = fdget(fd);
+                if (!f.file)
+                        return -EBADF;
+
+                vfio_group = kvm_vfio_group_get_external_user(f.file);
+                fdput(f);
+
+                if (IS_ERR(vfio_group))
+                        return PTR_ERR(vfio_group);
+
+                ret = -ENOENT;
+
+                mutex_lock(&kv->lock);
+
+                list_for_each_entry(kvg, &kv->group_list, node) {
+                        if (kvg->vfio_group != vfio_group)
+                                continue;
+
+                        list_del(&kvg->node);
+                        kvm_vfio_group_put_external_user(kvg->vfio_group);
+                        kfree(kvg);
+                        ret = 0;
+                        break;
+                }
+
+                mutex_unlock(&kv->lock);
+
+                kvm_vfio_group_put_external_user(vfio_group);
+
+                return ret;
+        }
+
+        return -ENXIO;
+}
+
+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);
+        }
+
+        return -ENXIO;
+}
+
+static int kvm_vfio_has_attr(struct kvm_device *dev,
+                             struct kvm_device_attr *attr)
+{
+        switch (attr->group) {
+        case KVM_DEV_VFIO_GROUP:
+                switch (attr->attr) {
+                case KVM_DEV_VFIO_GROUP_ADD:
+                case KVM_DEV_VFIO_GROUP_DEL:
+                        return 0;
+                }
+
+                break;
+        }
+
+        return -ENXIO;
+}
+
+static void kvm_vfio_destroy(struct kvm_device *dev)
+{
+        struct kvm_vfio *kv = dev->private;
+        struct kvm_vfio_group *kvg, *tmp;
+
+        list_for_each_entry_safe(kvg, tmp, &kv->group_list, node) {
+                kvm_vfio_group_put_external_user(kvg->vfio_group);
+                list_del(&kvg->node);
+                kfree(kvg);
+        }
+
+        kfree(kv);
+        kfree(dev); /* alloc by kvm_ioctl_create_device, free by .destroy */
+}
+
+static int kvm_vfio_create(struct kvm_device *dev, u32 type)
+{
+        struct kvm_device *tmp;
+        struct kvm_vfio *kv;
+
+        /* Only one VFIO "device" per VM */
+        list_for_each_entry(tmp, &dev->kvm->devices, vm_node)
+                if (tmp->ops == &kvm_vfio_ops)
+                        return -EBUSY;
+
+        kv = kzalloc(sizeof(*kv), GFP_KERNEL);
+        if (!kv)
+                return -ENOMEM;
+
+        INIT_LIST_HEAD(&kv->group_list);
+        mutex_init(&kv->lock);
+
+        dev->private = kv;
+
+        return 0;
+}
+
+struct kvm_device_ops kvm_vfio_ops = {
+        .name = "kvm-vfio",
+        .create = kvm_vfio_create,
+        .destroy = kvm_vfio_destroy,
+        .set_attr = kvm_vfio_set_attr,
+        .has_attr = kvm_vfio_has_attr,
+};