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0001 config PAGE_EXTENSION
0002         bool "Extend memmap on extra space for more information on page"
0003         ---help---
0004           Extend memmap on extra space for more information on page. This
0005           could be used for debugging features that need to insert extra
0006           field for every page. This extension enables us to save memory
0007           by not allocating this extra memory according to boottime
0008           configuration.
0009 
0010 config DEBUG_PAGEALLOC
0011         bool "Debug page memory allocations"
0012         depends on DEBUG_KERNEL
0013         depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
0014         depends on !KMEMCHECK
0015         select PAGE_EXTENSION
0016         select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
0017         ---help---
0018           Unmap pages from the kernel linear mapping after free_pages().
0019           Depending on runtime enablement, this results in a small or large
0020           slowdown, but helps to find certain types of memory corruption.
0021 
0022           For architectures which don't enable ARCH_SUPPORTS_DEBUG_PAGEALLOC,
0023           fill the pages with poison patterns after free_pages() and verify
0024           the patterns before alloc_pages().  Additionally,
0025           this option cannot be enabled in combination with hibernation as
0026           that would result in incorrect warnings of memory corruption after
0027           a resume because free pages are not saved to the suspend image.
0028 
0029           By default this option will have a small overhead, e.g. by not
0030           allowing the kernel mapping to be backed by large pages on some
0031           architectures. Even bigger overhead comes when the debugging is
0032           enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
0033           command line parameter.
0034 
0035 config DEBUG_PAGEALLOC_ENABLE_DEFAULT
0036         bool "Enable debug page memory allocations by default?"
0037         default n
0038         depends on DEBUG_PAGEALLOC
0039         ---help---
0040           Enable debug page memory allocations by default? This value
0041           can be overridden by debug_pagealloc=off|on.
0042 
0043 config PAGE_POISONING
0044         bool "Poison pages after freeing"
0045         select PAGE_EXTENSION
0046         select PAGE_POISONING_NO_SANITY if HIBERNATION
0047         ---help---
0048           Fill the pages with poison patterns after free_pages() and verify
0049           the patterns before alloc_pages. The filling of the memory helps
0050           reduce the risk of information leaks from freed data. This does
0051           have a potential performance impact.
0052 
0053           Note that "poison" here is not the same thing as the "HWPoison"
0054           for CONFIG_MEMORY_FAILURE. This is software poisoning only.
0055 
0056           If unsure, say N
0057 
0058 config PAGE_POISONING_NO_SANITY
0059         depends on PAGE_POISONING
0060         bool "Only poison, don't sanity check"
0061         ---help---
0062            Skip the sanity checking on alloc, only fill the pages with
0063            poison on free. This reduces some of the overhead of the
0064            poisoning feature.
0065 
0066            If you are only interested in sanitization, say Y. Otherwise
0067            say N.
0068 
0069 config PAGE_POISONING_ZERO
0070         bool "Use zero for poisoning instead of random data"
0071         depends on PAGE_POISONING
0072         ---help---
0073            Instead of using the existing poison value, fill the pages with
0074            zeros. This makes it harder to detect when errors are occurring
0075            due to sanitization but the zeroing at free means that it is
0076            no longer necessary to write zeros when GFP_ZERO is used on
0077            allocation.
0078 
0079            If unsure, say N
0080         bool
0081 
0082 config DEBUG_PAGE_REF
0083         bool "Enable tracepoint to track down page reference manipulation"
0084         depends on DEBUG_KERNEL
0085         depends on TRACEPOINTS
0086         ---help---
0087           This is a feature to add tracepoint for tracking down page reference
0088           manipulation. This tracking is useful to diagnose functional failure
0089           due to migration failures caused by page reference mismatches.  Be
0090           careful when enabling this feature because it adds about 30 KB to the
0091           kernel code.  However the runtime performance overhead is virtually
0092           nil until the tracepoints are actually enabled.