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SubjectRe: [PATCH] [0/16] POISON: Intro
How does this overlap with the bad page quarantine that ia64 uses
following an MCA?


On Tue, Apr 07, 2009 at 05:09:56PM +0200, Andi Kleen wrote:
> Upcoming Intel CPUs have support for recovering from some memory errors. This
> requires the OS to declare a page "poisoned", kill the processes associated
> with it and avoid using it in the future. This patchkit implements
> the necessary infrastructure in the VM.
> To quote the overview comment:
> * High level machine check handler. Handles pages reported by the
> * hardware as being corrupted usually due to a 2bit ECC memory or cache
> * failure.
> *
> * This focusses on pages detected as corrupted in the background.
> * When the current CPU tries to consume corruption the currently
> * running process can just be killed directly instead. This implies
> * that if the error cannot be handled for some reason it's safe to
> * just ignore it because no corruption has been consumed yet. Instead
> * when that happens another machine check will happen.
> *
> * Handles page cache pages in various states. The tricky part
> * here is that we can access any page asynchronous to other VM
> * users, because memory failures could happen anytime and anywhere,
> * possibly violating some of their assumptions. This is why this code
> * has to be extremely careful. Generally it tries to use normal locking
> * rules, as in get the standard locks, even if that means the
> * error handling takes potentially a long time.
> *
> * Some of the operations here are somewhat inefficient and have non
> * linear algorithmic complexity, because the data structures have not
> * been optimized for this case. This is in particular the case
> * for the mapping from a vma to a process. Since this case is expected
> * to be rare we hope we can get away with this.
> The code consists of a the high level handler in mm/memory-failure.c,
> a new page poison bit and various checks in the VM to handle poisoned
> pages.
> The main target right now is KVM guests, but it works for all kinds
> of applications.
> For the KVM use there was need for a new signal type so that
> KVM can inject the machine check into the guest with the proper
> address. This in theory allows other applications to handle
> memory failures too. The expection is that near all applications
> won't do that, but some very specialized ones might.
> This is not fully complete yet, in particular there are still ways
> to access poison through various ways (crash dump, /proc/kcore etc.)
> that need to be plugged too.
> Also undoubtedly the high level handler still has bugs and cases
> it cannot recover from. For example nonlinear mappings deadlock right now
> and a few other cases lose references. Huge pages are not supported
> yet. Any additional testing, reviewing etc. welcome.
> The patch series requires the earlier x86 MCE feature series for the x86
> specific action optional part. The code can be tested without the x86 specific
> part using the injector, this only requires to enable the Kconfig entry
> manually in some Kconfig file (by default it is implicitely enabled
> by the architecture)
> -Andi
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