[PATCH v3 vfio 0/3] pds/vfio: Fixes for locking bugs

[PATCH v3 vfio 0/3] pds/vfio: Fixes for locking bugs

[Brett Creeley]

This series contains fixes for locking bugs in the recently introduced
pds-vfio-pci driver. There was an initial bug reported by Dan Carpenter
at:

https://lore.kernel.org/kvm/1f9bc27b-3de9-4891-9687-ba2820c1b390@moroto.mountain/

However, more locking bugs were found when looking into the previously
mentioned issue. So, all fixes are included in this series.

v3:
- Change reset lock from spinlock to mutex

v2:
https://lore.kernel.org/kvm/20231011230115.35719-1-brett.creeley@amd.com/
- Trim the OOPs in the patch commit messages
- Rework patch 3/3 to only unlock the spinlock once
- Destroy the state_mutex in the driver specific vfio_device_ops.release
  callback

v1:
https://lore.kernel.org/kvm/20230914191540.54946-1-brett.creeley@amd.com/

Brett Creeley (3):
  pds/vfio: Fix spinlock bad magic BUG
  pds/vfio: Fix mutex lock->magic != lock warning
  pds/vfio: Fix possible sleep while in atomic context

 drivers/vfio/pci/pds/pci_drv.c  |  4 ++--
 drivers/vfio/pci/pds/vfio_dev.c | 30 +++++++++++++++++++++---------
 drivers/vfio/pci/pds/vfio_dev.h |  2 +-
 3 files changed, 24 insertions(+), 12 deletions(-)

-- 
2.17.1

[PATCH v3 vfio 1/3] pds/vfio: Fix spinlock bad magic BUG

[Brett Creeley]

The following BUG was found when running on a kernel with
CONFIG_DEBUG_SPINLOCK=y set:

BUG: spinlock bad magic on CPU#2, bash/2481
 lock: 0xffff8d6052a88f50, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
Call Trace:
 <TASK>
 dump_stack_lvl+0x36/0x50
 do_raw_spin_lock+0x79/0xc0
 pds_vfio_reset+0x1d/0x60 [pds_vfio_pci]
 pci_reset_function+0x4b/0x70
 reset_store+0x5b/0xa0
 kernfs_fop_write_iter+0x137/0x1d0
 vfs_write+0x2de/0x410
 ksys_write+0x5d/0xd0
 do_syscall_64+0x3b/0x90
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

As shown, the .magic: 00000000, does not match the expected value. This
is because spin_lock_init() is never called for the reset_lock. Fix
this by calling spin_lock_init(&pds_vfio->reset_lock) when initializing
the device.

Signed-off-by: Brett Creeley <brett.creeley@amd.com>
Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
---
 drivers/vfio/pci/pds/vfio_dev.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/vfio/pci/pds/vfio_dev.c b/drivers/vfio/pci/pds/vfio_dev.c
index 649b18ee394b..c351f588fa13 100644
--- a/drivers/vfio/pci/pds/vfio_dev.c
+++ b/drivers/vfio/pci/pds/vfio_dev.c
@@ -155,6 +155,8 @@ static int pds_vfio_init_device(struct vfio_device *vdev)
 
 	pds_vfio->vf_id = vf_id;
 
+	spin_lock_init(&pds_vfio->reset_lock);
+
 	vdev->migration_flags = VFIO_MIGRATION_STOP_COPY | VFIO_MIGRATION_P2P;
 	vdev->mig_ops = &pds_vfio_lm_ops;
 	vdev->log_ops = &pds_vfio_log_ops;
-- 
2.17.1

RE: [PATCH v3 vfio 1/3] pds/vfio: Fix spinlock bad magic BUG

[Tian, Kevin]

> From: Brett Creeley <brett.creeley@amd.com>
> Sent: Saturday, October 28, 2023 6:37 AM
> 
> The following BUG was found when running on a kernel with
> CONFIG_DEBUG_SPINLOCK=y set:
> 
> BUG: spinlock bad magic on CPU#2, bash/2481
>  lock: 0xffff8d6052a88f50, .magic: 00000000, .owner: <none>/-1, .owner_cpu:
> 0
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x36/0x50
>  do_raw_spin_lock+0x79/0xc0
>  pds_vfio_reset+0x1d/0x60 [pds_vfio_pci]
>  pci_reset_function+0x4b/0x70
>  reset_store+0x5b/0xa0
>  kernfs_fop_write_iter+0x137/0x1d0
>  vfs_write+0x2de/0x410
>  ksys_write+0x5d/0xd0
>  do_syscall_64+0x3b/0x90
>  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
> 
> As shown, the .magic: 00000000, does not match the expected value. This
> is because spin_lock_init() is never called for the reset_lock. Fix
> this by calling spin_lock_init(&pds_vfio->reset_lock) when initializing
> the device.
> 
> Signed-off-by: Brett Creeley <brett.creeley@amd.com>
> Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>

is this patch still required with patch3?

Re: [PATCH v3 vfio 1/3] pds/vfio: Fix spinlock bad magic BUG

[Brett Creeley]

On 10/30/2023 11:13 PM, Tian, Kevin wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
> 
> 
>> From: Brett Creeley <brett.creeley@amd.com>
>> Sent: Saturday, October 28, 2023 6:37 AM
>>
>> The following BUG was found when running on a kernel with
>> CONFIG_DEBUG_SPINLOCK=y set:
>>
>> BUG: spinlock bad magic on CPU#2, bash/2481
>>   lock: 0xffff8d6052a88f50, .magic: 00000000, .owner: <none>/-1, .owner_cpu:
>> 0
>> Call Trace:
>>   <TASK>
>>   dump_stack_lvl+0x36/0x50
>>   do_raw_spin_lock+0x79/0xc0
>>   pds_vfio_reset+0x1d/0x60 [pds_vfio_pci]
>>   pci_reset_function+0x4b/0x70
>>   reset_store+0x5b/0xa0
>>   kernfs_fop_write_iter+0x137/0x1d0
>>   vfs_write+0x2de/0x410
>>   ksys_write+0x5d/0xd0
>>   do_syscall_64+0x3b/0x90
>>   entry_SYSCALL_64_after_hwframe+0x6e/0xd8
>>
>> As shown, the .magic: 00000000, does not match the expected value. This
>> is because spin_lock_init() is never called for the reset_lock. Fix
>> this by calling spin_lock_init(&pds_vfio->reset_lock) when initializing
>> the device.
>>
>> Signed-off-by: Brett Creeley <brett.creeley@amd.com>
>> Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
> 
> is this patch still required with patch3?

Good point. It's not required anymore since there is no spinlock.

Thanks,

Brett

[PATCH v3 vfio 2/3] pds/vfio: Fix mutex lock->magic != lock warning

[Brett Creeley]

The following BUG was found when running on a kernel with
CONFIG_DEBUG_MUTEXES=y set:

DEBUG_LOCKS_WARN_ON(lock->magic != lock)
RIP: 0010:mutex_trylock+0x10d/0x120
Call Trace:
 <TASK>
 ? __warn+0x85/0x140
 ? mutex_trylock+0x10d/0x120
 ? report_bug+0xfc/0x1e0
 ? handle_bug+0x3f/0x70
 ? exc_invalid_op+0x17/0x70
 ? asm_exc_invalid_op+0x1a/0x20
 ? mutex_trylock+0x10d/0x120
 ? mutex_trylock+0x10d/0x120
 pds_vfio_reset+0x3a/0x60 [pds_vfio_pci]
 pci_reset_function+0x4b/0x70
 reset_store+0x5b/0xa0
 kernfs_fop_write_iter+0x137/0x1d0
 vfs_write+0x2de/0x410
 ksys_write+0x5d/0xd0
 do_syscall_64+0x3b/0x90
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

As shown, lock->magic != lock. This is because
mutex_init(&pds_vfio->state_mutex) is called in the VFIO open path. So,
if a reset is initiated before the VFIO device is opened the mutex will
have never been initialized. Fix this by calling
mutex_init(&pds_vfio->state_mutex) in the VFIO init path.

Also, don't destroy the mutex on close because the device may
be re-opened, which would cause mutex to be uninitialized. Fix this by
implementing a driver specific vfio_device_ops.release callback that
destroys the mutex before calling vfio_pci_core_release_dev().

Signed-off-by: Brett Creeley <brett.creeley@amd.com>
Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
---
 drivers/vfio/pci/pds/vfio_dev.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/vfio/pci/pds/vfio_dev.c b/drivers/vfio/pci/pds/vfio_dev.c
index c351f588fa13..306b1c25f016 100644
--- a/drivers/vfio/pci/pds/vfio_dev.c
+++ b/drivers/vfio/pci/pds/vfio_dev.c
@@ -155,6 +155,7 @@ static int pds_vfio_init_device(struct vfio_device *vdev)
 
 	pds_vfio->vf_id = vf_id;
 
+	mutex_init(&pds_vfio->state_mutex);
 	spin_lock_init(&pds_vfio->reset_lock);
 
 	vdev->migration_flags = VFIO_MIGRATION_STOP_COPY | VFIO_MIGRATION_P2P;
@@ -170,6 +171,16 @@ static int pds_vfio_init_device(struct vfio_device *vdev)
 	return 0;
 }
 
+static void pds_vfio_release_device(struct vfio_device *vdev)
+{
+	struct pds_vfio_pci_device *pds_vfio =
+		container_of(vdev, struct pds_vfio_pci_device,
+			     vfio_coredev.vdev);
+
+	mutex_destroy(&pds_vfio->state_mutex);
+	vfio_pci_core_release_dev(vdev);
+}
+
 static int pds_vfio_open_device(struct vfio_device *vdev)
 {
 	struct pds_vfio_pci_device *pds_vfio =
@@ -181,7 +192,6 @@ static int pds_vfio_open_device(struct vfio_device *vdev)
 	if (err)
 		return err;
 
-	mutex_init(&pds_vfio->state_mutex);
 	pds_vfio->state = VFIO_DEVICE_STATE_RUNNING;
 	pds_vfio->deferred_reset_state = VFIO_DEVICE_STATE_RUNNING;
 
@@ -201,14 +211,13 @@ static void pds_vfio_close_device(struct vfio_device *vdev)
 	pds_vfio_put_save_file(pds_vfio);
 	pds_vfio_dirty_disable(pds_vfio, true);
 	mutex_unlock(&pds_vfio->state_mutex);
-	mutex_destroy(&pds_vfio->state_mutex);
 	vfio_pci_core_close_device(vdev);
 }
 
 static const struct vfio_device_ops pds_vfio_ops = {
 	.name = "pds-vfio",
 	.init = pds_vfio_init_device,
-	.release = vfio_pci_core_release_dev,
+	.release = pds_vfio_release_device,
 	.open_device = pds_vfio_open_device,
 	.close_device = pds_vfio_close_device,
 	.ioctl = vfio_pci_core_ioctl,
-- 
2.17.1

[PATCH v3 vfio 3/3] pds/vfio: Fix possible sleep while in atomic context

[Brett Creeley]

The driver could possibly sleep while in atomic context resulting
in the following call trace while CONFIG_DEBUG_ATOMIC_SLEEP=y is
set:

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:283
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 2817, name: bash
preempt_count: 1, expected: 0
RCU nest depth: 0, expected: 0
Call Trace:
 <TASK>
 dump_stack_lvl+0x36/0x50
 __might_resched+0x123/0x170
 mutex_lock+0x1e/0x50
 pds_vfio_put_lm_file+0x1e/0xa0 [pds_vfio_pci]
 pds_vfio_put_save_file+0x19/0x30 [pds_vfio_pci]
 pds_vfio_state_mutex_unlock+0x2e/0x80 [pds_vfio_pci]
 pci_reset_function+0x4b/0x70
 reset_store+0x5b/0xa0
 kernfs_fop_write_iter+0x137/0x1d0
 vfs_write+0x2de/0x410
 ksys_write+0x5d/0xd0
 do_syscall_64+0x3b/0x90
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

This can happen if pds_vfio_put_restore_file() and/or
pds_vfio_put_save_file() grab the mutex_lock(&lm_file->lock)
while the spin_lock(&pds_vfio->reset_lock) is held, which can
happen during while calling pds_vfio_state_mutex_unlock().

Fix this by changing the reset_lock to reset_mutex so there are no such
conerns. Also, make sure to destroy the reset_mutex in the driver specific
VFIO device release function.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/kvm/1f9bc27b-3de9-4891-9687-ba2820c1b390@moroto.mountain/
Signed-off-by: Brett Creeley <brett.creeley@amd.com>
Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>
---
 drivers/vfio/pci/pds/pci_drv.c  |  4 ++--
 drivers/vfio/pci/pds/vfio_dev.c | 15 ++++++++-------
 drivers/vfio/pci/pds/vfio_dev.h |  2 +-
 3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/vfio/pci/pds/pci_drv.c b/drivers/vfio/pci/pds/pci_drv.c
index ab4b5958e413..caffa1a2cf59 100644
--- a/drivers/vfio/pci/pds/pci_drv.c
+++ b/drivers/vfio/pci/pds/pci_drv.c
@@ -55,10 +55,10 @@ static void pds_vfio_recovery(struct pds_vfio_pci_device *pds_vfio)
 	 * VFIO_DEVICE_STATE_RUNNING.
 	 */
 	if (deferred_reset_needed) {
-		spin_lock(&pds_vfio->reset_lock);
+		mutex_lock(&pds_vfio->reset_mutex);
 		pds_vfio->deferred_reset = true;
 		pds_vfio->deferred_reset_state = VFIO_DEVICE_STATE_ERROR;
-		spin_unlock(&pds_vfio->reset_lock);
+		mutex_unlock(&pds_vfio->reset_mutex);
 	}
 }
 
diff --git a/drivers/vfio/pci/pds/vfio_dev.c b/drivers/vfio/pci/pds/vfio_dev.c
index 306b1c25f016..4c351c59d05a 100644
--- a/drivers/vfio/pci/pds/vfio_dev.c
+++ b/drivers/vfio/pci/pds/vfio_dev.c
@@ -29,7 +29,7 @@ struct pds_vfio_pci_device *pds_vfio_pci_drvdata(struct pci_dev *pdev)
 void pds_vfio_state_mutex_unlock(struct pds_vfio_pci_device *pds_vfio)
 {
 again:
-	spin_lock(&pds_vfio->reset_lock);
+	mutex_lock(&pds_vfio->reset_mutex);
 	if (pds_vfio->deferred_reset) {
 		pds_vfio->deferred_reset = false;
 		if (pds_vfio->state == VFIO_DEVICE_STATE_ERROR) {
@@ -39,23 +39,23 @@ void pds_vfio_state_mutex_unlock(struct pds_vfio_pci_device *pds_vfio)
 		}
 		pds_vfio->state = pds_vfio->deferred_reset_state;
 		pds_vfio->deferred_reset_state = VFIO_DEVICE_STATE_RUNNING;
-		spin_unlock(&pds_vfio->reset_lock);
+		mutex_unlock(&pds_vfio->reset_mutex);
 		goto again;
 	}
 	mutex_unlock(&pds_vfio->state_mutex);
-	spin_unlock(&pds_vfio->reset_lock);
+	mutex_unlock(&pds_vfio->reset_mutex);
 }
 
 void pds_vfio_reset(struct pds_vfio_pci_device *pds_vfio)
 {
-	spin_lock(&pds_vfio->reset_lock);
+	mutex_lock(&pds_vfio->reset_mutex);
 	pds_vfio->deferred_reset = true;
 	pds_vfio->deferred_reset_state = VFIO_DEVICE_STATE_RUNNING;
 	if (!mutex_trylock(&pds_vfio->state_mutex)) {
-		spin_unlock(&pds_vfio->reset_lock);
+		mutex_unlock(&pds_vfio->reset_mutex);
 		return;
 	}
-	spin_unlock(&pds_vfio->reset_lock);
+	mutex_unlock(&pds_vfio->reset_mutex);
 	pds_vfio_state_mutex_unlock(pds_vfio);
 }
 
@@ -156,7 +156,7 @@ static int pds_vfio_init_device(struct vfio_device *vdev)
 	pds_vfio->vf_id = vf_id;
 
 	mutex_init(&pds_vfio->state_mutex);
-	spin_lock_init(&pds_vfio->reset_lock);
+	mutex_init(&pds_vfio->reset_mutex);
 
 	vdev->migration_flags = VFIO_MIGRATION_STOP_COPY | VFIO_MIGRATION_P2P;
 	vdev->mig_ops = &pds_vfio_lm_ops;
@@ -178,6 +178,7 @@ static void pds_vfio_release_device(struct vfio_device *vdev)
 			     vfio_coredev.vdev);
 
 	mutex_destroy(&pds_vfio->state_mutex);
+	mutex_destroy(&pds_vfio->reset_mutex);
 	vfio_pci_core_release_dev(vdev);
 }
 
diff --git a/drivers/vfio/pci/pds/vfio_dev.h b/drivers/vfio/pci/pds/vfio_dev.h
index b8f2d667608f..e7b01080a1ec 100644
--- a/drivers/vfio/pci/pds/vfio_dev.h
+++ b/drivers/vfio/pci/pds/vfio_dev.h
@@ -18,7 +18,7 @@ struct pds_vfio_pci_device {
 	struct pds_vfio_dirty dirty;
 	struct mutex state_mutex; /* protect migration state */
 	enum vfio_device_mig_state state;
-	spinlock_t reset_lock; /* protect reset_done flow */
+	struct mutex reset_mutex; /* protect reset_done flow */
 	u8 deferred_reset;
 	enum vfio_device_mig_state deferred_reset_state;
 	struct notifier_block nb;
-- 
2.17.1

RE: [PATCH v3 vfio 3/3] pds/vfio: Fix possible sleep while in atomic context

[Tian, Kevin]

> From: Brett Creeley <brett.creeley@amd.com>
> Sent: Saturday, October 28, 2023 6:37 AM
> 
> The driver could possibly sleep while in atomic context resulting
> in the following call trace while CONFIG_DEBUG_ATOMIC_SLEEP=y is
> set:
> 
> BUG: sleeping function called from invalid context at
> kernel/locking/mutex.c:283
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 2817, name: bash
> preempt_count: 1, expected: 0
> RCU nest depth: 0, expected: 0
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x36/0x50
>  __might_resched+0x123/0x170
>  mutex_lock+0x1e/0x50
>  pds_vfio_put_lm_file+0x1e/0xa0 [pds_vfio_pci]
>  pds_vfio_put_save_file+0x19/0x30 [pds_vfio_pci]
>  pds_vfio_state_mutex_unlock+0x2e/0x80 [pds_vfio_pci]
>  pci_reset_function+0x4b/0x70
>  reset_store+0x5b/0xa0
>  kernfs_fop_write_iter+0x137/0x1d0
>  vfs_write+0x2de/0x410
>  ksys_write+0x5d/0xd0
>  do_syscall_64+0x3b/0x90
>  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
> 
> This can happen if pds_vfio_put_restore_file() and/or
> pds_vfio_put_save_file() grab the mutex_lock(&lm_file->lock)
> while the spin_lock(&pds_vfio->reset_lock) is held, which can
> happen during while calling pds_vfio_state_mutex_unlock().
> 
> Fix this by changing the reset_lock to reset_mutex so there are no such
> conerns. Also, make sure to destroy the reset_mutex in the driver specific
> VFIO device release function.
> 
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/kvm/1f9bc27b-3de9-4891-9687-
> ba2820c1b390@moroto.mountain/
> Signed-off-by: Brett Creeley <brett.creeley@amd.com>
> Reviewed-by: Shannon Nelson <shannon.nelson@amd.com>

better change all three drivers together...