From: Michal Schmidt <mschmidt@redhat.com>

[ Upstream commit 4821d563cd7f251ae728be1a6d04af82a294a5b9 ]

Commit a7075f501bd3 ("ixgbevf: fix mailbox API compatibility by
negotiating supported features") added the .negotiate_features callback
to ixgbe_mac_operations and populated it in ixgbevf_mac_ops, but forgot
to add it to ixgbevf_hv_mac_ops. This leaves the function pointer NULL
on Hyper-V VMs.

During probe, ixgbevf_negotiate_api() calls ixgbevf_set_features(),
which unconditionally dereferences hw->mac.ops.negotiate_features().
On Hyper-V this results in a NULL pointer dereference:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  [...]
  Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine [...]
  Workqueue: events work_for_cpu_fn
  RIP: 0010:0x0
  [...]
  Call Trace:
   ixgbevf_negotiate_api+0x66/0x160 [ixgbevf]
   ixgbevf_sw_init+0xe4/0x1f0 [ixgbevf]
   ixgbevf_probe+0x20f/0x4a0 [ixgbevf]
   local_pci_probe+0x50/0xa0
   work_for_cpu_fn+0x1a/0x30
   [...]

Add ixgbevf_hv_negotiate_features_vf() that returns -EOPNOTSUPP and
wire it into ixgbevf_hv_mac_ops. The caller already handles -EOPNOTSUPP
gracefully.

Fixes: a7075f501bd3 ("ixgbevf: fix mailbox API compatibility by negotiating supported features")
Reported-by: Xiaoqiang Xiong <xxiong@redhat.com>
Closes: https://issues.redhat.com/browse/RHEL-155455
Assisted-by: Claude:claude-4.6-opus-high Cursor
Tested-by: Xiaoqiang Xiong <xxiong@redhat.com>
Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Error: Failed to generate final synthesis

 drivers/net/ethernet/intel/ixgbevf/vf.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/ethernet/intel/ixgbevf/vf.c b/drivers/net/ethernet/intel/ixgbevf/vf.c
index b67b580f7f1c9..f6df86d124b9e 100644
--- a/drivers/net/ethernet/intel/ixgbevf/vf.c
+++ b/drivers/net/ethernet/intel/ixgbevf/vf.c
@@ -709,6 +709,12 @@ static int ixgbevf_negotiate_features_vf(struct ixgbe_hw *hw, u32 *pf_features)
 	return err;
 }
 
+static int ixgbevf_hv_negotiate_features_vf(struct ixgbe_hw *hw,
+					    u32 *pf_features)
+{
+	return -EOPNOTSUPP;
+}
+
 /**
  *  ixgbevf_set_vfta_vf - Set/Unset VLAN filter table address
  *  @hw: pointer to the HW structure
@@ -1142,6 +1148,7 @@ static const struct ixgbe_mac_operations ixgbevf_hv_mac_ops = {
 	.setup_link		= ixgbevf_setup_mac_link_vf,
 	.check_link		= ixgbevf_hv_check_mac_link_vf,
 	.negotiate_api_version	= ixgbevf_hv_negotiate_api_version_vf,
+	.negotiate_features	= ixgbevf_hv_negotiate_features_vf,
 	.set_rar		= ixgbevf_hv_set_rar_vf,
 	.update_mc_addr_list	= ixgbevf_hv_update_mc_addr_list_vf,
 	.update_xcast_mode	= ixgbevf_hv_update_xcast_mode,
-- 
2.53.0