1 config PAGE_EXTENSION 2 bool "Extend memmap on extra space for more information on page" 3 ---help--- 4 Extend memmap on extra space for more information on page. This 5 could be used for debugging features that need to insert extra 6 field for every page. This extension enables us to save memory 7 by not allocating this extra memory according to boottime 8 configuration. 9 10 config DEBUG_PAGEALLOC 11 bool "Debug page memory allocations" 12 depends on DEBUG_KERNEL 13 depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC 14 depends on !KMEMCHECK 15 select PAGE_EXTENSION 16 select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC 17 ---help--- 18 Unmap pages from the kernel linear mapping after free_pages(). 19 Depending on runtime enablement, this results in a small or large 20 slowdown, but helps to find certain types of memory corruption. 21 22 For architectures which don't enable ARCH_SUPPORTS_DEBUG_PAGEALLOC, 23 fill the pages with poison patterns after free_pages() and verify 24 the patterns before alloc_pages(). Additionally, 25 this option cannot be enabled in combination with hibernation as 26 that would result in incorrect warnings of memory corruption after 27 a resume because free pages are not saved to the suspend image. 28 29 By default this option will have a small overhead, e.g. by not 30 allowing the kernel mapping to be backed by large pages on some 31 architectures. Even bigger overhead comes when the debugging is 32 enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc 33 command line parameter. 34 35 config DEBUG_PAGEALLOC_ENABLE_DEFAULT 36 bool "Enable debug page memory allocations by default?" 37 default n 38 depends on DEBUG_PAGEALLOC 39 ---help--- 40 Enable debug page memory allocations by default? This value 41 can be overridden by debug_pagealloc=off|on. 42 43 config PAGE_POISONING 44 bool "Poison pages after freeing" 45 select PAGE_EXTENSION 46 select PAGE_POISONING_NO_SANITY if HIBERNATION 47 ---help--- 48 Fill the pages with poison patterns after free_pages() and verify 49 the patterns before alloc_pages. The filling of the memory helps 50 reduce the risk of information leaks from freed data. This does 51 have a potential performance impact. 52 53 Note that "poison" here is not the same thing as the "HWPoison" 54 for CONFIG_MEMORY_FAILURE. This is software poisoning only. 55 56 If unsure, say N 57 58 config PAGE_POISONING_NO_SANITY 59 depends on PAGE_POISONING 60 bool "Only poison, don't sanity check" 61 ---help--- 62 Skip the sanity checking on alloc, only fill the pages with 63 poison on free. This reduces some of the overhead of the 64 poisoning feature. 65 66 If you are only interested in sanitization, say Y. Otherwise 67 say N. 68 69 config PAGE_POISONING_ZERO 70 bool "Use zero for poisoning instead of random data" 71 depends on PAGE_POISONING 72 ---help--- 73 Instead of using the existing poison value, fill the pages with 74 zeros. This makes it harder to detect when errors are occurring 75 due to sanitization but the zeroing at free means that it is 76 no longer necessary to write zeros when GFP_ZERO is used on 77 allocation. 78 79 If unsure, say N 80 bool 81 82 config DEBUG_PAGE_REF 83 bool "Enable tracepoint to track down page reference manipulation" 84 depends on DEBUG_KERNEL 85 depends on TRACEPOINTS 86 ---help--- 87 This is a feature to add tracepoint for tracking down page reference 88 manipulation. This tracking is useful to diagnose functional failure 89 due to migration failures caused by page reference mismatches. Be 90 careful when enabling this feature because it adds about 30 KB to the 91 kernel code. However the runtime performance overhead is virtually 92 nil until the tracepoints are actually enabled.