Andi Kleen 9b1beaf2b5 x86, mce: support action-optional machine checks ... Newer Intel CPUs support a new class of machine checks called recoverable action optional. Action Optional means that the CPU detected some form of corruption in the background and tells the OS about using a machine check exception. The OS can then take appropiate action, like killing the process with the corrupted data or logging the event properly to disk. This is done by the new generic high level memory failure handler added in a earlier patch. The high level handler takes the address with the failed memory and does the appropiate action, like killing the process. In this version of the patch the high level handler is stubbed out with a weak function to not create a direct dependency on the hwpoison branch. The high level handler cannot be directly called from the machine check exception though, because it has to run in a defined process context to be able to sleep when taking VM locks (it is not expected to sleep for a long time, just do so in some exceptional cases like lock contention) Thus the MCE handler has to queue a work item for process context, trigger process context and then call the high level handler from there. This patch adds two path to process context: through a per thread kernel exit notify_user() callback or through a high priority work item. The first runs when the process exits back to user space, the other when it goes to sleep and there is no higher priority process. The machine check handler will schedule both, and whoever runs first will grab the event. This is done because quick reaction to this event is critical to avoid a potential more fatal machine check when the corruption is consumed. There is a simple lock less ring buffer to queue the corrupted addresses between the exception handler and the process context handler. Then in process context it just calls the high level VM code with the corrupted PFNs. The code adds the required code to extract the failed address from the CPU's machine check registers. It doesn't try to handle all possible cases -- the specification has 6 different ways to specify memory address -- but only the linear address. Most of the required checking has been already done earlier in the mce_severity rule checking engine. Following the Intel recommendations Action Optional errors are only enabled for known situations (encoded in MCACODs). The errors are ignored otherwise, because they are action optional. v2: Improve comment, disable preemption while processing ring buffer (reported by Ying Huang) Signed-off-by: Andi Kleen <ak@linux.intel.com> Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>		2009-06-03 14:48:59 -07:00
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asm	x86, mce: support action-optional machine checks	2009-06-03 14:48:59 -07:00