[PATCH iwl-net] ice: fix VSI lists confusion when adding VLANs

[Michal Schmidt <mschmidt@redhat.com>]

The description of function ice_find_vsi_list_entry says:
  Search VSI list map with VSI count 1

However, since the blamed commit (see Fixes below), the function no
longer checks vsi_count. This causes a problem in ice_add_vlan_internal,
where the decision to share VSI lists between filter rules relies on the
vsi_count of the found existing VSI list being 1.

The reproducing steps:
1. Have a PF and two VFs.
   There will be a filter rule for VLAN 0, refering to a VSI list
   containing VSIs: 0 (PF), 2 (VF#0), 3 (VF#1).
2. Add VLAN 1234 to VF#0.
   ice will make the wrong decision to share the VSI list with the new
   rule. The wrong behavior may not be immediately apparent, but it can
   be observed with debug prints.
3. Add VLAN 1234 to VF#1.
   ice will unshare the VSI list for the VLAN 1234 rule. Due to the
   earlier bad decision, the newly created VSI list will contain
   VSIs 0 (PF) and 3 (VF#1), instead of expected 2 (VF#0) and 3 (VF#1).
4. Try pinging a network peer over the VLAN interface on VF#0.
   This fails.

Reproducer script at:
https://gitlab.com/mschmidt2/repro/-/blob/master/RHEL-46814/test-vlan-vsi-list-confusion.sh
Commented debug trace:
https://gitlab.com/mschmidt2/repro/-/blob/master/RHEL-46814/ice-vlan-vsi-lists-debug.txt
Patch adding the debug prints:
https://gitlab.com/mschmidt2/linux/-/commit/f8a8814623944a45091a77c6094c40bfe726bfdb

One thing I'm not certain about is the implications for the LAG feature,
which is another caller of ice_find_vsi_list_entry. I don't have a
LAG-capable card at hand to test.

Fixes: 25746e4f06a5 ("ice: changes to the interface with the HW and FW for SRIOV_VF+LAG")
Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
---
 drivers/net/ethernet/intel/ice/ice_switch.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_switch.c b/drivers/net/ethernet/intel/ice/ice_switch.c
index fe8847184cb1..4e6e7af962bd 100644
--- a/drivers/net/ethernet/intel/ice/ice_switch.c
+++ b/drivers/net/ethernet/intel/ice/ice_switch.c
@@ -3264,7 +3264,7 @@ ice_find_vsi_list_entry(struct ice_hw *hw, u8 recp_id, u16 vsi_handle,
 
 	list_head = &sw->recp_list[recp_id].filt_rules;
 	list_for_each_entry(list_itr, list_head, list_entry) {
-		if (list_itr->vsi_list_info) {
+		if (list_itr->vsi_count == 1 && list_itr->vsi_list_info) {
 			map_info = list_itr->vsi_list_info;
 			if (test_bit(vsi_handle, map_info->vsi_map)) {
 				*vsi_list_id = map_info->vsi_list_id;
-- 
2.45.2