[v2,3/9] vfio: New external user group/file match

Commit Message

Alex Williamson June 19, 2017, 5:14 p.m. UTC

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 <[e-mail]>
Reviewed-by: Eric Auger <[e-mail]>
Reviewed-by: Paolo Bonzini <[e-mail]>
Cc: [e-mail]
---
 drivers/vfio/vfio.c  |    9 +++++++++
 include/linux/vfio.h |    2 ++
 virt/kvm/vfio.c      |   27 +++++++++++++++++++--------
 3 files changed, 30 insertions(+), 8 deletions(-)

Comments

kernel test robot June 20, 2017, 5:01 a.m. UTC | #1

Hi Alex,

[auto build test ERROR on vfio/next]
[also build test ERROR on v4.12-rc6 next-20170619]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Alex-Williamson/vfio-Fix-release-ordering-races-and-use-driver_override/20170620-095741
base:   https://github.com/awilliam/linux-vfio.git next
config: powerpc-defconfig (attached as .config)
compiler: powerpc64-linux-gnu-gcc (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=powerpc 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All errors (new ones prefixed by >>):

   arch/powerpc/kvm/../../../virt/kvm/vfio.c: In function 'kvm_vfio_set_attr':
>> arch/powerpc/kvm/../../../virt/kvm/vfio.c:262:4: error: 'vfio_group' may be used uninitialized in this function [-Werror=maybe-uninitialized]
       kvm_spapr_tce_release_vfio_group(dev->kvm, vfio_group);
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   arch/powerpc/kvm/../../../virt/kvm/vfio.c:190:21: note: 'vfio_group' was declared here
     struct vfio_group *vfio_group;
                        ^~~~~~~~~~
   cc1: all warnings being treated as errors

vim +/vfio_group +262 arch/powerpc/kvm/../../../virt/kvm/vfio.c

600c6bde Alex Williamson 2017-06-19  256  								f.file))
ec53500f Alex Williamson 2013-10-30  257  				continue;
ec53500f Alex Williamson 2013-10-30  258  
ec53500f Alex Williamson 2013-10-30  259  			list_del(&kvg->node);
14979b3f Alex Williamson 2017-06-19  260  			kvm_arch_end_assignment(dev->kvm);
14979b3f Alex Williamson 2017-06-19  261  #ifdef CONFIG_SPAPR_TCE_IOMMU
14979b3f Alex Williamson 2017-06-19 @262  			kvm_spapr_tce_release_vfio_group(dev->kvm, vfio_group);
14979b3f Alex Williamson 2017-06-19  263  #endif
14979b3f Alex Williamson 2017-06-19  264  			kvm_vfio_group_set_kvm(kvg->vfio_group, NULL);
ec53500f Alex Williamson 2013-10-30  265  			kvm_vfio_group_put_external_user(kvg->vfio_group);

:::::: The code at line 262 was first introduced by commit
:::::: 14979b3f26fbbe87d4240e463db53e64dd127184 kvm-vfio: Decouple only when we match a group

:::::: TO: Alex Williamson <[e-mail]>
:::::: CC: 0day robot <[e-mail]>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

Patch

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 54dd2fbf83d9..7597a377eb4e 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -1776,6 +1776,15 @@  void vfio_group_put_external_user(struct vfio_group *group)
 }
 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);
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index edf9b2cad277..9b34d0af5d27 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -97,6 +97,8 @@  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);
diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
index f1b0b7bca9a9..9aba73127aac 100644
--- a/virt/kvm/vfio.c
+++ b/virt/kvm/vfio.c
@@ -51,6 +51,22 @@  static struct vfio_group *kvm_vfio_group_get_external_user(struct file *filep)
 	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 *);
@@ -231,18 +247,13 @@  static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
 		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);
@@ -259,7 +270,7 @@  static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
 
 		mutex_unlock(&kv->lock);
 
-		kvm_vfio_group_put_external_user(vfio_group);
+		fdput(f);
 
 		kvm_vfio_update_coherency(dev);