This is a note to let you know that I've just added the patch titled vfio: New external user group/file match to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: vfio-new-external-user-group-file-match.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 5d6dee80a1e94cc284d03e06d930e60e8d3ecf7d Mon Sep 17 00:00:00 2001 From: Alex Williamson <alex.williamson@xxxxxxxxxx> Date: Wed, 28 Jun 2017 13:50:05 -0600 Subject: vfio: New external user group/file match From: Alex Williamson <alex.williamson@xxxxxxxxxx> 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@xxxxxxxxxx> Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Tested-by: Eric Auger <eric.auger@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -1587,6 +1587,15 @@ 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 @@ -85,6 +85,8 @@ 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 @@ -47,6 +47,22 @@ 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 *); @@ -171,18 +187,13 @@ 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); @@ -196,7 +207,7 @@ 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); Patches currently in stable-queue which might be from alex.williamson@xxxxxxxxxx are queue-4.4/vfio-new-external-user-group-file-match.patch queue-4.4/vfio-fix-group-release-deadlock.patch