Control how to kill processes when uncorrected memory error (typically a 2bit error in a memory module) is detected in the background by hardware that cannot be handled by the kernel. In some cases (like the page still having a valid copy on disk) the kernel will handle the failure transparently without affecting any applications. But if there is no other up-to-date copy of the data it will kill to prevent any data corruptions from propagating.
1: Kill all processes that have the corrupted and not reloadable page mapped as soon as the corruption is detected. Note this is not supported for a few types of pages, like kernel internally allocated data or the swap cache, but works for the majority of user pages.
0: Only unmap the corrupted page from all processes and only kill a process who tries to access it.
The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can handle this if they want to.
This is only active on architectures/platforms with advanced machine check handling and depends on the hardware capabilities.
Applications can override this setting individually with the PR_MCE_KILL prctl