[PATCH 3.16 065/192] vfio: New external user group/file match

Ben Hutchings
2017-10-09T13:20:29Z

From: Alex Williamson <alex.williamson@redhat.com>

commit 5d6dee80a1e94cc284d03e06d930e60e8d3ecf7d upstream.

At the point where the kvm-vfio pseudo device wants to release its
vfio group reference, we can't always acquire a new reference to make
that happen. The group can be in a state where we wouldn't allow a
new reference to be added. This new helper function allows a caller
to match a file to a group to facilitate this. Given a file and
group, report if they match. Thus the caller needs to already have a
group reference to match to the file. This allows the deletion of a
group without acquiring a new reference.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/vfio/vfio.c | 9 +++++++++
include/linux/vfio.h | 2 ++
virt/kvm/vfio.c | 27 +++++++++++++++++++--------
3 files changed, 30 insertions(+), 8 deletions(-)

--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -1436,6 +1436,15 @@ void vfio_group_put_external_user(struct
}
EXPORT_SYMBOL_GPL(vfio_group_put_external_user);

+bool vfio_external_group_match_file(struct vfio_group *test_group,
+ struct file *filep)
+{
+ struct vfio_group *group = filep->private_data;
+
+ return (filep->f_op == &vfio_group_fops) && (group == test_group);
+}
+EXPORT_SYMBOL_GPL(vfio_external_group_match_file);
+
int vfio_external_user_iommu_id(struct vfio_group *group)
{
return iommu_group_id(group->iommu_group);
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -94,6 +94,8 @@ extern void vfio_unregister_iommu_driver
*/
extern struct vfio_group *vfio_group_get_external_user(struct file *filep);
extern void vfio_group_put_external_user(struct vfio_group *group);
+extern bool vfio_external_group_match_file(struct vfio_group *group,
+ struct file *filep);
extern int vfio_external_user_iommu_id(struct vfio_group *group);
extern long vfio_external_check_extension(struct vfio_group *group,
unsigned long arg);
--- a/virt/kvm/vfio.c
+++ b/virt/kvm/vfio.c
@@ -46,6 +46,22 @@ static struct vfio_group *kvm_vfio_group
return vfio_group;
}

+static bool kvm_vfio_external_group_match_file(struct vfio_group *group,
+ struct file *filep)
+{
+ bool ret, (*fn)(struct vfio_group *, struct file *);
+
+ fn = symbol_get(vfio_external_group_match_file);
+ if (!fn)
+ return false;
+
+ ret = fn(group, filep);
+
+ symbol_put(vfio_external_group_match_file);
+
+ return ret;
+}
+
static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
{
void (*fn)(struct vfio_group *);
@@ -168,18 +184,13 @@ static int kvm_vfio_set_group(struct kvm
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)
+ if (!kvm_vfio_external_group_match_file(kvg->vfio_group,
+ f.file))
continue;

list_del(&kvg->node);
@@ -191,7 +202,7 @@ static int kvm_vfio_set_group(struct kvm

mutex_unlock(&kv->lock);

- kvm_vfio_group_put_external_user(vfio_group);
+ fdput(f);

kvm_vfio_update_coherency(dev);