[PATCH v4 7/9] s390/vfio-ap: Fix hot-unplug skipped when last AP adapter or domain removed

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

The vfio_ap_mdev_hot_unplug_cfg() function uses the return value of
bitmap_andnot() to determine whether the guest APCB needs to be updated.
However, bitmap_andnot() returns false when the resulting destination
bitmap is empty. This means that if the only adapter, domain or control
domain assigned to an mdev is removed from the host's AP configuration,
the bit is correctly cleared from the shadow APCB, but bitmap_andnot()
returns false because the result is an empty bitmap. Consequently,
do_hotplug remains 0 and vfio_ap_mdev_update_guest_apcb() is never called,
leaving the KVM guest with stale hardware access to the unplugged AP
devices.

Fix this by replacing the bitmap_andnot() return value check with
bitmap_intersects() to determine whether the shadow APCB actually
overlaps with the removal mask. If there is an intersection, call
bitmap_andnot() solely for its side effect of clearing the bits, then
unconditionally set do_hotplug to trigger the guest APCB update.

Fixes: eeb386aeb5b7c ("s390/vfio-ap: handle config changed and scan complete notification")
Cc: stable@vger.kernel.org
Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_ops.c | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index d667ad4bbf70..16779cfc64e8 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -2568,24 +2568,28 @@ static void vfio_ap_mdev_hot_unplug_cfg(struct ap_matrix_mdev *matrix_mdev,
 					unsigned long *aqrem,
 					unsigned long *cdrem)
 {
-	int do_hotplug = 0;
+	bool do_hotplug = false;
 
-	if (!bitmap_empty(aprem, AP_DEVICES)) {
-		do_hotplug |= bitmap_andnot(matrix_mdev->shadow_apcb.apm,
-					    matrix_mdev->shadow_apcb.apm,
-					    aprem, AP_DEVICES);
+	if (bitmap_intersects(matrix_mdev->shadow_apcb.apm, aprem, AP_DEVICES)) {
+		bitmap_andnot(matrix_mdev->shadow_apcb.apm,
+			      matrix_mdev->shadow_apcb.apm,
+			      aprem, AP_DEVICES);
+		do_hotplug = true;
 	}
 
-	if (!bitmap_empty(aqrem, AP_DOMAINS)) {
-		do_hotplug |= bitmap_andnot(matrix_mdev->shadow_apcb.aqm,
-					    matrix_mdev->shadow_apcb.aqm,
-					    aqrem, AP_DEVICES);
+	if (bitmap_intersects(matrix_mdev->shadow_apcb.aqm, aqrem, AP_DOMAINS)) {
+		bitmap_andnot(matrix_mdev->shadow_apcb.aqm,
+			      matrix_mdev->shadow_apcb.aqm,
+			      aqrem, AP_DOMAINS);
+		do_hotplug = true;
 	}
 
-	if (!bitmap_empty(cdrem, AP_DOMAINS))
-		do_hotplug |= bitmap_andnot(matrix_mdev->shadow_apcb.adm,
-					    matrix_mdev->shadow_apcb.adm,
-					    cdrem, AP_DOMAINS);
+	if (bitmap_intersects(matrix_mdev->shadow_apcb.adm, cdrem, AP_DOMAINS)) {
+		bitmap_andnot(matrix_mdev->shadow_apcb.adm,
+			      matrix_mdev->shadow_apcb.adm,
+			      cdrem, AP_DOMAINS);
+		do_hotplug = true;
+	}
 
 	if (do_hotplug)
 		vfio_ap_mdev_update_guest_apcb(matrix_mdev);
-- 
2.53.0