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Subject: ibv_devinfo -ve max_mcast_qp_attach value with MLX4 driver - known issue?
Date: Fri, 31 Jul 2020 16:14:35 -0700
Message-ID: <> (raw)


I have a CX3/IB card (MLX4 driver) assigned to a Xen VM and notice the 
following with/without the below patch applied. Is this a known issue 
and are there any fixes available for it? I couldn't find any references 
to it and thought I should check with the list/author. I do not see this 
issue with baremetal or KVM, but only on a Xen VM. Thanks.

1. ibv_devinfo with patch a40ded604365 applied (all other HCA attribs 
are OK):/
# ibv_devinfo -v | grep max_mcast_qp_attach/
/max_mcast_qp_attach: -8

2. ibv_devinfo without patch a40ded604365 applied:/
///# ibv_devinfo -v | grep max_mcast_qp_attach/
/max_mcast_qp_attach: 248
/ /


commit a40ded6043658444ee4dd6ee374119e4e98b33fc
Author: Aya Levin <>
Date:   Tue Jan 22 15:19:44 2019 +0200

     net/mlx4_core: Add masking for a few queries on HCA caps

     Driver reads the query HCA capabilities without the corresponding 
     Without the correct masks, the base addresses of the queues are
     unaligned.  In addition some reserved bits were wrongly read.  
Using the
     correct masks, ensures alignment of the base addresses and allows 
     firmware versions safe use of the reserved bits.

     Fixes: ab9c17a009ee ("mlx4_core: Modify driver initialization flow 
to accommodate SRIOV for Ethernet")
     Fixes: 0ff1fb654bec ("{NET, IB}/mlx4: Add device managed flow 
steering firmware API")
     Signed-off-by: Aya Levin <>
     Signed-off-by: Tariq Toukan <>
     Signed-off-by: David S. Miller <>


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