1. 30 May, 2018 1 commit
    • NeilBrown's avatar
      MIPS: c-r4k: Fix data corruption related to cache coherence · aa9a00ef
      NeilBrown authored
      commit 55a2aa08 upstream.
      
      When DMA will be performed to a MIPS32 1004K CPS, the L1-cache for the
      range needs to be flushed and invalidated first.
      The code currently takes one of two approaches.
      1/ If the range is less than the size of the dcache, then HIT type
         requests flush/invalidate cache lines for the particular addresses.
         HIT-type requests a globalised by the CPS so this is safe on SMP.
      
      2/ If the range is larger than the size of dcache, then INDEX type
         requests flush/invalidate the whole cache. INDEX type requests affect
         the local cache only. CPS does not propagate them in any way. So this
         invalidation is not safe on SMP CPS systems.
      
      Data corruption due to '2' can quite easily be demonstrated by
      repeatedly "echo 3 > /proc/sys/vm/drop_caches" and then sha1sum a file
      that is several times the size of available memory. Dropping caches
      means that large contiguous extents (large than dcache) are more likely.
      
      This was not a problem before Linux-4.8 because option 2 was never used
      if CONFIG_MIPS_CPS was defined. The commit which removed that apparently
      didn't appreciate the full consequence of the change.
      
      We could, in theory, globalize the INDEX based flush by sending an IPI
      to other cores. These cache invalidation routines can be called with
      interrupts disabled and synchronous IPI require interrupts to be
      enabled. Asynchronous IPI may not trigger writeback soon enough. So we
      cannot use IPI in practice.
      
      We can already test if IPI would be needed for an INDEX operation with
      r4k_op_needs_ipi(R4K_INDEX). If this is true then we mustn't try the
      INDEX approach as we cannot use IPI. If this is false (e.g. when there
      is only one core and hence one L1 cache) then it is safe to use the
      INDEX approach without IPI.
      
      This patch avoids options 2 if r4k_op_needs_ipi(R4K_INDEX), and so
      eliminates the corruption.
      
      Fixes: c00ab489 ("MIPS: Remove cpu_has_safe_index_cacheops")
      Signed-off-by: default avatarNeilBrown <neil@brown.name>
      Cc: Ralf Baechle <ralf@linux-mips.org>
      Cc: Paul Burton <paul.burton@mips.com>
      Cc: linux-mips@linux-mips.org
      Cc: <stable@vger.kernel.org> # 4.8+
      Patchwork: https://patchwork.linux-mips.org/patch/19259/Signed-off-by: default avatarJames Hogan <jhogan@kernel.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      aa9a00ef
  2. 25 May, 2018 39 commits