• David Daney's avatar
    MIPS: Implement Read Inhibit/eXecute Inhibit · 6dd9344c
    David Daney authored
    The SmartMIPS ASE specifies how Read Inhibit (RI) and eXecute Inhibit
    (XI) bits in the page tables work.  The upper two bits of EntryLo{0,1}
    are RI and XI when the feature is enabled in the PageGrain register.
    SmartMIPS only covers 32-bit systems.  Cavium Octeon+ extends this to
    64-bit systems by continuing to place the RI and XI bits in the top of
    EntryLo even when EntryLo is 64-bits wide.
    
    Because we need to carry the RI and XI bits in the PTE, the layout of
    the PTE is changed.  There is a two instruction overhead in the TLB
    refill hot path to get the EntryLo bits into the proper position.
    Also the TLB load exception has to probe the TLB to check if RI or XI
    caused the exception.
    
    Also of note is that the layout of the PTE bits is done at compile and
    runtime rather than statically.  In the 32-bit case this allows for
    the same number of PFN bits as before the patch as the _PAGE_HUGE is
    not supported in 32-bit kernels (we have _PAGE_NO_EXEC and
    _PAGE_NO_READ instead of _PAGE_READ and _PAGE_HUGE).
    
    The patch is tested on Cavium Octeon+, but should also work on 32-bit
    systems with the Smart-MIPS ASE.
    Signed-off-by: default avatarDavid Daney <ddaney@caviumnetworks.com>
    To: linux-mips@linux-mips.org
    Patchwork: http://patchwork.linux-mips.org/patch/952/
    Patchwork: http://patchwork.linux-mips.org/patch/956/
    Patchwork: http://patchwork.linux-mips.org/patch/962/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
    6dd9344c
pgtable.h 11.7 KB