Skip to content
  1. May 18, 2016
    • shamir rabinovitch's avatar
      IB/mlx4: Fix unaligned access in send_reply_to_slave · 04ef0f1a
      shamir rabinovitch authored
      
      
      The problem is that the function 'send_reply_to_slave' gets the
      'req_sa_mad' as a pointer whose address is only aliged to 4 bytes
      but is 8 bytes in size.  This can result in unaligned access faults
      on certain architectures.
      
      Sowmini Varadhan pointed to this reply from Dave Miller that say
      that memcpy should not be used to solve alignment issues:
      https://lkml.org/lkml/2015/10/21/352
      
      Optimization of memcpy to 'ldx' instruction can only happen if the
      compiler knows that the size of the data we are copying is 8 bytes
      and it assumes it is aligned to 8 bytes. If the compiler know the
      type is not aligned to 8 it must not optimize the 8 byte copy.
      Defining the data type as aligned to 4 forces the compiler to treat
      all accesses as though they aren't aligned and avoids the 'ldx'
      optimization.
      
      Full credit for the idea goes to Jason Gunthorpe
      <jgunthorpe@obsidianresearch.com>.
      
      Signed-off-by: default avatarShamir Rabinovitch <shamir.rabinovitch@oracle.com>
      Signed-off-by: default avatarDoug Ledford <dledford@redhat.com>
      04ef0f1a
  2. May 14, 2016