Re: [PATCH v2 3/8] s390/vfio-ap: Fix use of wrong lock in mdev probe function

[Anthony Krowiak <akrowiak@linux.ibm.com>]

On 8/11/26 11:58 AM, Matthew Rosato wrote:
> On 8/10/26 3:22 PM, Anthony Krowiak wrote:
>> The vfio_ap_mdev_probe function uses the matrix_dev->mdevs_lock
>> mutex to guard the add of a newly created ap_matrix_mdev object to the
>> matrix_dev->mdev_list. This mutex does not protect against traversal
>> of the list; its purpose is to guard against concurrent access to fields
>> contained in an ap_matrix_mdev object. This could lead to kernel memory
>> corruption or use-after-free if another mdev is created concurrently.
>>
>> The adding of an ap_matrix_mdev object to matrix_dev->mdev_list
>> is now guarded by the matrix_dev->guests_lock which is the correct
>> way to protect against concurrent mdev_list access.
>>
>> See the vfio-ap-locking.rst in the linux kernel tree.
>>
>> Fixes: 2c1ee8983aa3 ("s390/vfio-ap: prepare for dynamic update of guest's APCB on queue probe/remove")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
>> ---
>>   drivers/s390/crypto/vfio_ap_ops.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
>> index e382e5a1cb99..a472de00bc14 100644
>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>> @@ -803,9 +803,9 @@ static int vfio_ap_mdev_probe(struct mdev_device *mdev)
>>   	matrix_mdev->req_trigger = NULL;
>>   	matrix_mdev->cfg_chg_trigger = NULL;
>>   	dev_set_drvdata(&mdev->dev, matrix_mdev);
>> -	mutex_lock(&matrix_dev->mdevs_lock);
>> +	mutex_lock(&matrix_dev->guests_lock);
> Sashiko reports that this patch introduces a regression, which seems valid.
>
> AFAICT you resolve this regression with patch 7 of this series.
>
> For the sake of bisect, can you look at whether squashing these 2
> patches together would work so that we don't have an interim regression?

The reason for the two different patches is because the shah on the 
Fixes: tag
differ.

>
>