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authorAndi Kleen <ak@linux.intel.com>2009-10-03 20:28:42 -0400
committerAndi Kleen <ak@linux.intel.com>2009-10-03 21:23:26 -0400
commitf58ee00f1547ceb17b610ecfce2aa9097f1f9737 (patch)
treed7be3b1e0d0d05c2f4b6016b79ab52fff8abf934 /Documentation/vm/hwpoison.txt
parent1087e9b4ff708976499b4de541d9e1d57d49b60a (diff)
HWPOISON: Add brief hwpoison description to Documentation
Signed-off-by: Andi Kleen <ak@linux.intel.com>
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1What is hwpoison?
2
3Upcoming Intel CPUs have support for recovering from some memory errors
4(``MCA recovery''). This requires the OS to declare a page "poisoned",
5kill the processes associated with it and avoid using it in the future.
6
7This patchkit implements the necessary infrastructure in the VM.
8
9To quote the overview comment:
10
11 * High level machine check handler. Handles pages reported by the
12 * hardware as being corrupted usually due to a 2bit ECC memory or cache
13 * failure.
14 *
15 * This focusses on pages detected as corrupted in the background.
16 * When the current CPU tries to consume corruption the currently
17 * running process can just be killed directly instead. This implies
18 * that if the error cannot be handled for some reason it's safe to
19 * just ignore it because no corruption has been consumed yet. Instead
20 * when that happens another machine check will happen.
21 *
22 * Handles page cache pages in various states. The tricky part
23 * here is that we can access any page asynchronous to other VM
24 * users, because memory failures could happen anytime and anywhere,
25 * possibly violating some of their assumptions. This is why this code
26 * has to be extremely careful. Generally it tries to use normal locking
27 * rules, as in get the standard locks, even if that means the
28 * error handling takes potentially a long time.
29 *
30 * Some of the operations here are somewhat inefficient and have non
31 * linear algorithmic complexity, because the data structures have not
32 * been optimized for this case. This is in particular the case
33 * for the mapping from a vma to a process. Since this case is expected
34 * to be rare we hope we can get away with this.
35
36The code consists of a the high level handler in mm/memory-failure.c,
37a new page poison bit and various checks in the VM to handle poisoned
38pages.
39
40The main target right now is KVM guests, but it works for all kinds
41of applications. KVM support requires a recent qemu-kvm release.
42
43For the KVM use there was need for a new signal type so that
44KVM can inject the machine check into the guest with the proper
45address. This in theory allows other applications to handle
46memory failures too. The expection is that near all applications
47won't do that, but some very specialized ones might.
48
49---
50
51There are two (actually three) modi memory failure recovery can be in:
52
53vm.memory_failure_recovery sysctl set to zero:
54 All memory failures cause a panic. Do not attempt recovery.
55 (on x86 this can be also affected by the tolerant level of the
56 MCE subsystem)
57
58early kill
59 (can be controlled globally and per process)
60 Send SIGBUS to the application as soon as the error is detected
61 This allows applications who can process memory errors in a gentle
62 way (e.g. drop affected object)
63 This is the mode used by KVM qemu.
64
65late kill
66 Send SIGBUS when the application runs into the corrupted page.
67 This is best for memory error unaware applications and default
68 Note some pages are always handled as late kill.
69
70---
71
72User control:
73
74vm.memory_failure_recovery
75 See sysctl.txt
76
77vm.memory_failure_early_kill
78 Enable early kill mode globally
79
80PR_MCE_KILL
81 Set early/late kill mode/revert to system default
82 arg1: PR_MCE_KILL_CLEAR: Revert to system default
83 arg1: PR_MCE_KILL_SET: arg2 defines thread specific mode
84 PR_MCE_KILL_EARLY: Early kill
85 PR_MCE_KILL_LATE: Late kill
86 PR_MCE_KILL_DEFAULT: Use system global default
87PR_MCE_KILL_GET
88 return current mode
89
90
91---
92
93Testing:
94
95madvise(MADV_POISON, ....)
96 (as root)
97 Poison a page in the process for testing
98
99
100hwpoison-inject module through debugfs
101 /sys/debug/hwpoison/corrupt-pfn
102
103Inject hwpoison fault at PFN echoed into this file
104
105
106Architecture specific MCE injector
107
108x86 has mce-inject, mce-test
109
110Some portable hwpoison test programs in mce-test, see blow.
111
112---
113
114References:
115
116http://halobates.de/mce-lc09-2.pdf
117 Overview presentation from LinuxCon 09
118
119git://git.kernel.org/pub/scm/utils/cpu/mce/mce-test.git
120 Test suite (hwpoison specific portable tests in tsrc)
121
122git://git.kernel.org/pub/scm/utils/cpu/mce/mce-inject.git
123 x86 specific injector
124
125
126---
127
128Limitations:
129
130- Not all page types are supported and never will. Most kernel internal
131objects cannot be recovered, only LRU pages for now.
132- Right now hugepage support is missing.
133
134---
135Andi Kleen, Oct 2009
136