Re: [PATCH v2 1/2] s390/vfio-ap: fix hang during removal of mdev after duplicate assignment

[Anthony Krowiak]

On 8/18/22 10:12 AM, Halil Pasic wrote:
> On Thu, 18 Aug 2022 09:26:05 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> Subject: s390/vfio-ap: fix hang during removal of mdev after duplicate
> assignment
>
> It would have made sense to do it this way in the first place, even
> if the link code were to take care of the duplicates. It did not really
> make sense to do the whole filtering biz and everything else.


No, it did not; however, nobody caught it in review either. In fact, 
this probably should have been done prior to hot plug.


>   Maybe we
> should spin the short description and the rest of the commit message so
> it reflects the code more.


I'm not sure what you mean here, are you suggesting the first two 
paragraphs should be eliminated?


>   
>
> > When the same adapter or domain is assigned more than one time prior to
> > removing the matrix mdev to which it is assigned, the remove operation
> > will hang. The reason is because the same vfio_ap_queue objects with an
> > APQN containing the APID of the adapter or APQI of the domain being
> > assigned will get added to the hashtable that holds them multiple times.
> > This results in the pprev and next pointers of the hlist_node (mdev_qnode
> > field in the vfio_ap_queue object) pointing to the queue object itself.
> > This causes an interminable loop when the mdev is removed and the queue
> > table is iterated to reset the queues.
> >
> > To fix this problem, the assignment operation is bypassed when assigning
> > an adapter or domain if it is already assigned to the matrix mdev.
> >
> > Since it is not necessary to assign a resource already assigned or to
> > unassign a resource that has not been assigned, this patch will bypass
> > all assignment/unassignment operations for an adapter, domain or
> > control domain under these circumstances.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: 771e387d5e79 ("s390/vfio-ap: manage link between queue struct and matrix mdev")
> Not 11cb2419fafe ("s390/vfio-ap: manage link between queue struct and
> matrix mdev")
>
> Is my repo borked?
>
>
> > Reported-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> > Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> > ---
> >   drivers/s390/crypto/vfio_ap_ops.c | 30 ++++++++++++++++++++++++++++++
> >   1 file changed, 30 insertions(+)
> >
> > diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> > index 6c8c41fac4e1..ee82207b4e60 100644
> > --- a/drivers/s390/crypto/vfio_ap_ops.c
> > +++ b/drivers/s390/crypto/vfio_ap_ops.c
> > @@ -984,6 +984,11 @@ static ssize_t assign_adapter_store(struct device *dev,
> >   		goto done;
> >   	}
> >   
> > +	if (test_bit_inv(apid, matrix_mdev->matrix.apm)) {
> > +		ret = count;
> > +		goto done;
> > +	}
> > +
> >   	set_bit_inv(apid, matrix_mdev->matrix.apm);
> >   
> >   	ret = vfio_ap_mdev_validate_masks(matrix_mdev);
> > @@ -1109,6 +1114,11 @@ static ssize_t unassign_adapter_store(struct device *dev,
> >   		goto done;
> >   	}
> >   
> > +	if (!test_bit_inv(apid, matrix_mdev->matrix.apm)) {
> > +		ret = count;
> > +		goto done;
> > +	}
> > +
> >   	clear_bit_inv((unsigned long)apid, matrix_mdev->matrix.apm);
> >   	vfio_ap_mdev_hot_unplug_adapter(matrix_mdev, apid);
> >   	ret = count;
> > @@ -1183,6 +1193,11 @@ static ssize_t assign_domain_store(struct device *dev,
> >   		goto done;
> >   	}
> >   
> > +	if (test_bit_inv(apqi, matrix_mdev->matrix.aqm)) {
> > +		ret = count;
> > +		goto done;
> > +	}
> > +
> >   	set_bit_inv(apqi, matrix_mdev->matrix.aqm);
> >   
> >   	ret = vfio_ap_mdev_validate_masks(matrix_mdev);
> > @@ -1286,6 +1301,11 @@ static ssize_t unassign_domain_store(struct device *dev,
> >   		goto done;
> >   	}
> >   
> > +	if (!test_bit_inv(apqi, matrix_mdev->matrix.aqm)) {
> > +		ret = count;
> > +		goto done;
> > +	}
> > +
> >   	clear_bit_inv((unsigned long)apqi, matrix_mdev->matrix.aqm);
> >   	vfio_ap_mdev_hot_unplug_domain(matrix_mdev, apqi);
> >   	ret = count;
> > @@ -1329,6 +1349,11 @@ static ssize_t assign_control_domain_store(struct device *dev,
> >   		goto done;
> >   	}
> >   
> > +	if (test_bit_inv(id, matrix_mdev->matrix.adm)) {
> > +		ret = count;
> > +		goto done;
> > +	}
> > +
> >   	/* Set the bit in the ADM (bitmask) corresponding to the AP control
> >   	 * domain number (id). The bits in the mask, from most significant to
> >   	 * least significant, correspond to IDs 0 up to the one less than the
> > @@ -1378,6 +1403,11 @@ static ssize_t unassign_control_domain_store(struct device *dev,
> >   		goto done;
> >   	}
> >   
> > +	if (!test_bit_inv(domid, matrix_mdev->matrix.adm)) {
> > +		ret = count;
> > +		goto done;
> > +	}
> > +
> >   	clear_bit_inv(domid, matrix_mdev->matrix.adm);
> >   
> >   	if (test_bit_inv(domid, matrix_mdev->shadow_apcb.adm)) {