• Jason Gunthorpe's avatar
    RDMA/ucontext: Add a core API for mmaping driver IO memory · 5f9794dc
    Jason Gunthorpe authored
    To support disassociation and PCI hot unplug, we have to track all the
    VMAs that refer to the device IO memory. When disassociation occurs the
    VMAs have to be revised to point to the zero page, not the IO memory, to
    allow the physical HW to be unplugged.
    
    The three drivers supporting this implemented three different versions
    of this algorithm, all leaving something to be desired. This new common
    implementation has a few differences from the driver versions:
    
    - Track all VMAs, including splitting/truncating/etc. Tie the lifetime of
      the private data allocation to the lifetime of the vma. This avoids any
      tricks with setting vm_ops which Linus didn't like. (see link)
    - Support multiple mms, and support properly tracking mmaps triggered by
      processes other than the one first opening the uverbs fd. This makes
      fork behavior of disassociation enabled drivers the same as fork support
      in normal drivers.
    - Don't use crazy get_task stuff.
    - Simplify the approach for to racing between vm_ops close and
      disassociation, fixing the related bugs most of the driver
      implementations had. Since we are in core code the tracking list can be
      placed in struct ib_uverbs_ufile, which has a lifetime strictly longer
      than any VMAs created by mmap on the uverbs FD.
    
    Link: https://www.spinics.net/lists/stable/msg248747.html
    Link: https://lkml.kernel.org/r/CA+55aFxJTV_g46AQPoPXen-UPiqR1HGMZictt7VpC-SMFbm3Cw@mail.gmail.comSigned-off-by: 's avatarJason Gunthorpe <jgg@mellanox.com>
    Signed-off-by: 's avatarLeon Romanovsky <leonro@mellanox.com>
    Signed-off-by: 's avatarDoug Ledford <dledford@redhat.com>
    5f9794dc
uverbs.h 11.9 KB