linux-libre/mm/Kconfig.debug

config PAGE_EXTENSION
	bool "Extend memmap on extra space for more information on page"
	---help---
	  Extend memmap on extra space for more information on page. This
	  could be used for debugging features that need to insert extra
	  field for every page. This extension enables us to save memory
	  by not allocating this extra memory according to boottime
	  configuration.

config DEBUG_PAGEALLOC
	bool "Debug page memory allocations"
	depends on DEBUG_KERNEL
	depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
	depends on !KMEMCHECK
	select PAGE_EXTENSION
	select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
	---help---
	  Unmap pages from the kernel linear mapping after free_pages().
	  Depending on runtime enablement, this results in a small or large
	  slowdown, but helps to find certain types of memory corruption.

	  For architectures which don't enable ARCH_SUPPORTS_DEBUG_PAGEALLOC,
	  fill the pages with poison patterns after free_pages() and verify
	  the patterns before alloc_pages().  Additionally,
	  this option cannot be enabled in combination with hibernation as
	  that would result in incorrect warnings of memory corruption after
	  a resume because free pages are not saved to the suspend image.

	  By default this option will have a small overhead, e.g. by not
	  allowing the kernel mapping to be backed by large pages on some
	  architectures. Even bigger overhead comes when the debugging is
	  enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
	  command line parameter.

config DEBUG_PAGEALLOC_ENABLE_DEFAULT
	bool "Enable debug page memory allocations by default?"
	default n
	depends on DEBUG_PAGEALLOC
	---help---
	  Enable debug page memory allocations by default? This value
	  can be overridden by debug_pagealloc=off|on.

config PAGE_POISONING
	bool "Poison pages after freeing"
	select PAGE_EXTENSION
	select PAGE_POISONING_NO_SANITY if HIBERNATION
	---help---
	  Fill the pages with poison patterns after free_pages() and verify
	  the patterns before alloc_pages. The filling of the memory helps
	  reduce the risk of information leaks from freed data. This does
	  have a potential performance impact.

	  Note that "poison" here is not the same thing as the "HWPoison"
	  for CONFIG_MEMORY_FAILURE. This is software poisoning only.

	  If unsure, say N

config PAGE_POISONING_NO_SANITY
	depends on PAGE_POISONING
	bool "Only poison, don't sanity check"
	---help---
	   Skip the sanity checking on alloc, only fill the pages with
	   poison on free. This reduces some of the overhead of the
	   poisoning feature.

	   If you are only interested in sanitization, say Y. Otherwise
	   say N.

config PAGE_POISONING_ZERO
	bool "Use zero for poisoning instead of random data"
	depends on PAGE_POISONING
	---help---
	   Instead of using the existing poison value, fill the pages with
	   zeros. This makes it harder to detect when errors are occurring
	   due to sanitization but the zeroing at free means that it is
	   no longer necessary to write zeros when GFP_ZERO is used on
	   allocation.

	   If unsure, say N
	bool

config DEBUG_PAGE_REF
	bool "Enable tracepoint to track down page reference manipulation"
	depends on DEBUG_KERNEL
	depends on TRACEPOINTS
	---help---
	  This is a feature to add tracepoint for tracking down page reference
	  manipulation. This tracking is useful to diagnose functional failure
	  due to migration failures caused by page reference mismatches.  Be
	  careful when enabling this feature because it adds about 30 KB to the
	  kernel code.  However the runtime performance overhead is virtually
	  nil until the tracepoints are actually enabled.