1. 10 Aug, 2009 1 commit
    • Linus Torvalds's avatar
      x86: Fix serialization in pit_expect_msb() · b6e61eef
      Linus Torvalds authored
      
      
      Wei Chong Tan reported a fast-PIT-calibration corner-case:
      
      | pit_expect_msb() is vulnerable to SMI disturbance corner case
      | in some platforms which causes /proc/cpuinfo to show wrong
      | CPU MHz value when quick_pit_calibrate() jumps to success
      | section.
      
      I think that the real issue isn't even an SMI - but the fact
      that in the very last iteration of the loop, there's no
      serializing instruction _after_ the last 'rdtsc'. So even in
      the absense of SMI's, we do have a situation where the cycle
      counter was read without proper serialization.
      
      The last check should be done outside the outer loop, since
      _inside_ the outer loop, we'll be testing that the PIT has
      the right MSB value has the right value in the next iteration.
      
      So only the _last_ iteration is special, because that's the one
      that will not check the PIT MSB value any more, and because the
      final 'get_cycles()' isn't serialized.
      
      In other words:
      
       - I'd like to move the PIT MSB check to after the last
         iteration, rather than in every iteration
      
       - I think we should comment on the fact that it's also a
         serializing instruction and so 'fences in' the TSC read.
      
      Here's a suggested replacement.
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Reported-by: default avatar"Tan, Wei Chong" <wei.chong.tan@intel.com>
      Tested-by: default avatar"Tan, Wei Chong" <wei.chong.tan@intel.com>
      LKML-Reference: <B28277FD4E0F9247A3D55704C440A140D5D683F3@pgsmsx504.gar.corp.intel.com>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      b6e61eef
  2. 09 Aug, 2009 12 commits
  3. 08 Aug, 2009 8 commits
  4. 07 Aug, 2009 19 commits