February 25, 2019

Yes, that’s the scenario in the sentences I excerpted from the article. The OS can then take appropriate action, like killing the process with the corrupted data or logging the event properly to disk. Ongoing evolution of Linux x86 machine check handling at LinuxCon If I’m not mistaken, that’s the processor family this article was referring to. Potentially corrupted processes can then be located by finding all processes that have the corrupted page mapped. Thus, poisoned dirty pages may have important data corruption.

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Now flip ihtel me to page and look at what SRAO errors are architecturally defined, there in section Alternatively, memory may be occasionally “scrubbed.

In a more serious vein, I found the onjector less clear and more hard to read than the usual material on the kernel page. Machine check handling on Linux paperslides for Linux Kongress MCE is the mechanism by which the hardware reports the bad page to the operating system.


These delays include asynchronous hardware reporting of the machine check event, How can a machine check for accessing erroneous memory contents be asynchronous? These delays include asynchronous hardware reporting of the machine check event, and delayed execution of the handler via a workqueue.

Towards an improved error reporting infrastructure intwl Linux. Includes an overview of modern mcelog. So there we have it.


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Was something in the engineers’ infrastructure missing the fifth bits due to faulty memory perhaps? ECC is able to recover from multib i y te errors Posted Dec 4, 9: But that’s not the case the article describes. This code snippet on the linked page illustrates some of the “action optional” machine check exceptions: Memory “poisoning”, with its delayed handling of errors, allows for a more graceful recovery from and isolation of uncorrected memory errors rather than just crashing the system.

However, dirty pages in the page cache are recovered by invalidation of the cache. However, this is infeasible for two reasons.

EDAC is an alternative approach at reporting memory errors. Recovery of uncorrected recoverable machine check errors is an enhancement in machine-check architecture. In either case, the hardware doesn’t immediately cause a machine check but rather flags the data unit as poisoned until read or consumed. Posted Aug 28, 7: If the erroneous injcetor is never read, no machine check is necessary.

I found a different Linux EDAC project on sourceforge. Thus, poisoned dirty pages may have important data corruption. The blanket action of ibtel the machine for all uncorrected soft and hard memory errors is sometimes over-reactive. Huge pages fail since reverse mapping is not supported to identify the process which owns the page.


Newer Intel CPUs support a new class of machine checks called recoverable action optional. To offset this increased error rate, recent processors have included support for “poisoned” memory, an adaptive method for flagging and recovering from memory errors. Please consider signing up for a subscription and helping to keep LWN publishing August 26, If the faulting word is due to a prefetch, or is late in the cache line that was read due to a demand fetch, that data may arrive at the CPU quite long after the instruction that triggered that line fill.

This link is broken. Since these pages have a duplicate backing copy on disk, the in-memory cache copy can be invalidated.

How can the CPU continue executing and generate a machine check at some arbitrarily later time? This simple harness uses debugfs to allow failures at an arbitrary page to be injected. The OS marks the memory as poisoned, or otherwise discards the contents of the page if it was clean. For these uncorrectable errors, the hardware typically generates inkector trap which, in turn, causes a kernel panic.