linux-stable.git/drivers/vfio/mdev/mdev_sysfs.c, branch linux-5.10.y

vfio/mdev: Do not allow a mdev_type to have a NULL parent pointer

2021-05-14T07:50:26+00:00

[ Upstream commit b5a1f8921d5040bb788492bf33a66758021e4be5 ]

There is a small race where the parent is NULL even though the kobj has
already been made visible in sysfs.

For instance the attribute_group is made visible in sysfs_create_files()
and the mdev_type_attr_show() does:

    ret = attr->show(kobj, type->parent->dev, buf);

Which will crash on NULL parent. Move the parent setup to before the type
pointer leaves the stack frame.

Fixes: 7b96953bc640 ("vfio: Mediated device Core driver")
Reviewed-by: Christoph Hellwig 
Reviewed-by: Kevin Tian 
Reviewed-by: Max Gurtovoy 
Reviewed-by: Cornelia Huck 
Signed-off-by: Jason Gunthorpe 
Message-Id: <2-v2-d36939638fc6+d54-vfio2_jgg@nvidia.com>
Signed-off-by: Alex Williamson 
Signed-off-by: Sasha Levin

vfio/mdev: Fix reference count leak in add_mdev_supported_type

2020-05-29T22:07:18+00:00

kobject_init_and_add() takes reference even when it fails.
If this function returns an error, kobject_put() must be called to
properly clean up the memory associated with the object. Thus,
replace kfree() by kobject_put() to fix this issue. Previous
commit "b8eb718348b8" fixed a similar problem.

Fixes: 7b96953bc640 ("vfio: Mediated device Core driver")
Signed-off-by: Qiushi Wu 
Reviewed-by: Cornelia Huck 
Reviewed-by: Kirti Wankhede 
Signed-off-by: Alex Williamson

vfio/mdev: make create attribute static

2020-01-09T18:30:57+00:00

The create attribute is not exported, so make it
static to avoid the following sparse warning:

drivers/vfio/mdev/mdev_sysfs.c:77:1: warning: symbol 'mdev_type_attr_create' was not declared. Should it be static?

Signed-off-by: Ben Dooks (Codethink) 
Reviewed-by: Cornelia Huck 
Signed-off-by: Alex Williamson

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500

2019-06-19T15:09:55+00:00

Based on 2 normalized pattern(s):

  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

  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 #

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-only

has been chosen to replace the boilerplate/reference in 4122 file(s).

Signed-off-by: Thomas Gleixner 
Reviewed-by: Enrico Weigelt 
Reviewed-by: Kate Stewart 
Reviewed-by: Allison Randal 
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de
Signed-off-by: Greg Kroah-Hartman

vfio/mdev: Avoid creating sysfs remove file on stale device removal

2019-06-06T18:32:37+00:00

If device is removal is initiated by two threads as below, mdev core
attempts to create a syfs remove file on stale device.
During this flow, below [1] call trace is observed.

     cpu-0                                    cpu-1
     -----                                    -----
  mdev_unregister_device()
    device_for_each_child
       mdev_device_remove_cb
          mdev_device_remove
                                       user_syscall
                                         remove_store()
                                           mdev_device_remove()
                                        [..]
   unregister device();
                                       /* not found in list or
                                        * active=false.
                                        */
                                          sysfs_create_file()
                                          ..Call trace

Now that mdev core follows correct device removal sequence of the linux
bus model, remove shouldn't fail in normal cases. If it fails, there is
no point of creating a stale file or checking for specific error status.

kernel: WARNING: CPU: 2 PID: 9348 at fs/sysfs/file.c:327
sysfs_create_file_ns+0x7f/0x90
kernel: CPU: 2 PID: 9348 Comm: bash Kdump: loaded Not tainted
5.1.0-rc6-vdevbus+ #6
kernel: Hardware name: Supermicro SYS-6028U-TR4+/X10DRU-i+, BIOS 2.0b
08/09/2016
kernel: RIP: 0010:sysfs_create_file_ns+0x7f/0x90
kernel: Call Trace:
kernel: remove_store+0xdc/0x100 [mdev]
kernel: kernfs_fop_write+0x113/0x1a0
kernel: vfs_write+0xad/0x1b0
kernel: ksys_write+0x5a/0xe0
kernel: do_syscall_64+0x5a/0x210
kernel: entry_SYSCALL_64_after_hwframe+0x49/0xbe

Reviewed-by: Cornelia Huck 
Signed-off-by: Parav Pandit 
Signed-off-by: Alex Williamson

vfio/mdev: Improve the create/remove sequence

2019-06-06T16:52:32+00:00

This patch addresses below two issues and prepares the code to address
3rd issue listed below.

1. mdev device is placed on the mdev bus before it is created in the
vendor driver. Once a device is placed on the mdev bus without creating
its supporting underlying vendor device, mdev driver's probe() gets
triggered.  However there isn't a stable mdev available to work on.

   create_store()
     mdev_create_device()
       device_register()
          ...
         vfio_mdev_probe()
        [...]
        parent->ops->create()
          vfio_ap_mdev_create()
            mdev_set_drvdata(mdev, matrix_mdev);
            /* Valid pointer set above */

Due to this way of initialization, mdev driver who wants to use the mdev,
doesn't have a valid mdev to work on.

2. Current creation sequence is,
   parent->ops_create()
   groups_register()

Remove sequence is,
   parent->ops->remove()
   groups_unregister()

However, remove sequence should be exact mirror of creation sequence.
Once this is achieved, all users of the mdev will be terminated first
before removing underlying vendor device.
(Follow standard linux driver model).
At that point vendor's remove() ops shouldn't fail because taking the
device off the bus should terminate any usage.

3. When remove operation fails, mdev sysfs removal attempts to add the
file back on already removed device. Following call trace [1] is observed.

[1] call trace:
kernel: WARNING: CPU: 2 PID: 9348 at fs/sysfs/file.c:327 sysfs_create_file_ns+0x7f/0x90
kernel: CPU: 2 PID: 9348 Comm: bash Kdump: loaded Not tainted 5.1.0-rc6-vdevbus+ #6
kernel: Hardware name: Supermicro SYS-6028U-TR4+/X10DRU-i+, BIOS 2.0b 08/09/2016
kernel: RIP: 0010:sysfs_create_file_ns+0x7f/0x90
kernel: Call Trace:
kernel: remove_store+0xdc/0x100 [mdev]
kernel: kernfs_fop_write+0x113/0x1a0
kernel: vfs_write+0xad/0x1b0
kernel: ksys_write+0x5a/0xe0
kernel: do_syscall_64+0x5a/0x210
kernel: entry_SYSCALL_64_after_hwframe+0x49/0xbe

Therefore, mdev core is improved in following ways.

1. Split the device registration/deregistration sequence so that some
things can be done between initialization of the device and hooking it
up to the bus respectively after deregistering it from the bus but
before giving up our final reference.
In particular, this means invoking the ->create() and ->remove()
callbacks in those new windows. This gives the vendor driver an
initialized mdev device to work with during creation.
At the same time, a bus driver who wish to bind to mdev driver also
gets initialized mdev device.

This follows standard Linux kernel bus and device model.

2. During remove flow, first remove the device from the bus. This
ensures that any bus specific devices are removed.
Once device is taken off the mdev bus, invoke remove() of mdev
from the vendor driver.

3. The driver core device model provides way to register and auto
unregister the device sysfs attribute groups at dev->groups.
Make use of dev->groups to let core create the groups and eliminate
code to avoid explicit groups creation and removal.

To ensure, that new sequence is solid, a below stack dump of a
process is taken who attempts to remove the device while device is in
use by vfio driver and user application.
This stack dump validates that vfio driver guards against such device
removal when device is in use.

 cat /proc/21962/stack
[<0>] vfio_del_group_dev+0x216/0x3c0 [vfio]
[<0>] mdev_remove+0x21/0x40 [mdev]
[<0>] device_release_driver_internal+0xe8/0x1b0
[<0>] bus_remove_device+0xf9/0x170
[<0>] device_del+0x168/0x350
[<0>] mdev_device_remove_common+0x1d/0x50 [mdev]
[<0>] mdev_device_remove+0x8c/0xd0 [mdev]
[<0>] remove_store+0x71/0x90 [mdev]
[<0>] kernfs_fop_write+0x113/0x1a0
[<0>] vfs_write+0xad/0x1b0
[<0>] ksys_write+0x5a/0xe0
[<0>] do_syscall_64+0x5a/0x210
[<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[<0>] 0xffffffffffffffff

This prepares the code to eliminate calling device_create_file() in
subsequent patch.

Reviewed-by: Cornelia Huck 
Signed-off-by: Parav Pandit 
Signed-off-by: Alex Williamson

vfio/mdev: Follow correct remove sequence

2019-05-07T17:23:13+00:00

mdev_remove_sysfs_files() should follow exact mirror sequence of a
create, similar to what is followed in error unwinding path of
mdev_create_sysfs_files().

Fixes: 6a62c1dfb5c7 ("vfio/mdev: Re-order sysfs attribute creation")
Reviewed-by: Cornelia Huck 
Reviewed-by: Maxim Levitsky 
Signed-off-by: Parav Pandit 
Signed-off-by: Alex Williamson

vfio-mdev: Switch to use new generic UUID API

2019-02-05T18:51:56+00:00

There are new types and helpers that are supposed to be used in new code.

As a preparation to get rid of legacy types and API functions do
the conversion here.

Cc: Kirti Wankhede 
Cc: Alex Williamson 
Signed-off-by: Andy Shevchenko 
Reviewed-by: Christoph Hellwig 
Signed-off-by: Alex Williamson

vfio/mdev: add static modifier to add_mdev_supported_type

2018-12-12T19:59:48+00:00

Set add_mdev_supported_type as static since it is only used within
mdev_sysfs.c.  This fixes -Wmissing-prototypes gcc warning.

Signed-off-by: Paolo Cretaro 
Reviewed-by: Cornelia Huck 
Signed-off-by: Alex Williamson

vfio/mdev: Re-order sysfs attribute creation

2018-06-08T16:24:30+00:00

There exists a gap at the end of mdev_device_create() where the device
is visible to userspace, but we're not yet ready to handle removal, as
triggered through the 'remove' attribute.  We handle this properly in
mdev_device_remove() with an -EAGAIN return, but we can marginally
reduce this gap by adding this attribute as a final step of our sysfs
setup.

Reviewed-by: Kirti Wankhede 
Reviewed-by: Cornelia Huck 
Acked-by: Halil Pasic 
Signed-off-by: Alex Williamson