The current organization of the x86 documentation makes it appear as
if the "i386" documentation doesn't apply to x86-64, which is does.
Thus, move that documentation into Documentation/x86, and move the
x86-64-specific stuff into Documentation/x86/x86_64 with the eventual
goal to move stuff that isn't actually 64-bit specific back into
Documentation/x86.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

Background:
 The MCE handler has several paths that it can take, depending on various
 conditions of the MCE status and the value of the 'tolerant' knob.  The
 exact semantics are not well defined and the code is a bit twisty.

Description:
 This patch makes the MCE handler's behavior more clear by documenting the
 behavior for various 'tolerant' levels.  It also fixes or enhances
 several small things in the handler.  Specifically:
     * If RIPV is set it is not safe to restart, so set the 'no way out'
       flag rather than the 'kill it' flag.
     * Don't panic() on correctable MCEs.
     * If the _OVER bit is set *and* the _UC bit is set (meaning possibly
       dropped uncorrected errors), set the 'no way out' flag.
     * Use EIPV for testing whether an app can be killed (SIGBUS) rather
       than RIPV.  According to docs, EIPV indicates that the error is
       related to the IP, while RIPV simply means the IP is valid to
       restart from.
     * Don't clear the MCi_STATUS registers until after the panic() path.
       This leaves the status bits set after the panic() so clever BIOSes
       can find them (and dumb BIOSes can do nothing).

 This patch also calls nonseekable_open() in mce_open (as suggested by akpm).

Result:
 Tolerant levels behave almost identically to how they always have, but
 not it's well defined.  There's a slightly higher chance of panic()ing
 when multiple errors happen (a good thing, IMHO).  If you take an MBE and
 panic(), the error status bits are not cleared.

Alternatives:
 None.

Testing:
 I used software to inject correctable and uncorrectable errors.  With
 tolerant = 3, the system usually survives.  With tolerant = 2, the system
 usually panic()s (PCC) but not always.  With tolerant = 1, the system
 always panic()s.  When the system panic()s, the BIOS is able to detect
 that the cause of death was an MC4.  I was not able to reproduce the
 case of a non-PCC error in userspace, with EIPV, with (tolerant < 3).
 That will be rare at best.
Signed-off-by: NTim Hockin <thockin@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Background:
 We've found that MCEs (specifically DRAM SBEs) tend to come in bunches,
 especially when we are trying really hard to stress the system out.  The
 current MCE poller uses a static interval which does not care whether it
 has or has not found MCEs recently.

Description:
 This patch makes the MCE poller adjust the polling interval dynamically.
 If we find an MCE, poll 2x faster (down to 10 ms).  When we stop finding
 MCEs, poll 2x slower (up to check_interval seconds).  The check_interval
 tunable becomes the max polling interval.  The "Machine check events
 logged" printk() is rate limited to the check_interval, which should be
 identical behavior to the old functionality.

Result:
 If you start to take a lot of correctable errors (not exceptions), you
 log them faster and more accurately (less chance of overflowing the MCA
 registers).  If you don't take a lot of errors, you will see no change.

Alternatives:
 I considered simply reducing the polling interval to 10 ms immediately
 and keeping it there as long as we continue to find errors.  This felt a
 bit heavy handed, but does perform significantly better for the default
 check_interval of 5 minutes (we're using a few seconds when testing for
 DRAM errors).  I could be convinced to go with this, if anyone felt it
 was not too aggressive.

Testing:
 I used an error-injecting DIMM to create lots of correctable DRAM errors
 and verified that the polling interval accelerates.  The printk() only
 happens once per check_interval seconds.

Patch:
 This patch is against 2.6.21-rc7.
Signed-Off-By: NTim Hockin <thockin@google.com>
Signed-off-by: NAndi Kleen <ak@suse.de>

When a machine check event is detected (including a AMD RevF threshold
overflow event) allow to run a "trigger" program. This allows user space
to react to such events sooner.

The trigger is configured using a new trigger entry in the
machinecheck sysfs interface. It is currently shared between
all CPUs.

I also fixed the AMD threshold handler to run the machine
check polling code immediately to actually log any events
that might have caused the threshold interrupt.

Also added some documentation for the mce sysfs interface.
Signed-off-by: NAndi Kleen <ak@suse.de>