Commit 0e91a0c6 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

mm/highmem: Provide CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP 



CONFIG_DEBUG_KMAP_LOCAL, which is selected by CONFIG_DEBUG_HIGHMEM is only
providing guard pages, but does not provide a mechanism to enforce the
usage of the kmap_local() infrastructure.

Provide CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP which forces the temporary
mapping even for lowmem pages. This needs to be a seperate config switch
because this only works on architectures which do not have cache aliasing
problems.

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20201118204007.028261233@linutronix.de
parent 6e799cb6

lib/Kconfig.debug

+14 −0
Original line number Diff line number Diff line
@@ -856,9 +856,23 @@ config DEBUG_KMAP_LOCAL 
	  This option enables additional error checking for the kmap_local

	  infrastructure.  Disable for production use.



config ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP

	bool



config DEBUG_KMAP_LOCAL_FORCE_MAP

	bool "Enforce kmap_local temporary mappings"

	depends on DEBUG_KERNEL && ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP

	select KMAP_LOCAL

	select DEBUG_KMAP_LOCAL

	help

	  This option enforces temporary mappings through the kmap_local

	  mechanism for non-highmem pages and on non-highmem systems.

	  Disable this for production systems!



config DEBUG_HIGHMEM

	bool "Highmem debugging"

	depends on DEBUG_KERNEL && HIGHMEM

	select DEBUG_KMAP_LOCAL_FORCE_MAP if ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP

	select DEBUG_KMAP_LOCAL

	help

	  This option enables additional error checking for high memory

mm/highmem.c

+11 −1
Original line number Diff line number Diff line
@@ -474,7 +474,12 @@ void *__kmap_local_page_prot(struct page *page, pgprot_t prot) 
{

	void *kmap;



	if (!PageHighMem(page))

	/*

	 * To broaden the usage of the actual kmap_local() machinery always map

	 * pages when debugging is enabled and the architecture has no problems

	 * with alias mappings.

	 */

	if (!IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP) && !PageHighMem(page))

		return page_address(page);



	/* Try kmap_high_get() if architecture has it enabled */
@@ -494,6 +499,11 @@ void kunmap_local_indexed(void *vaddr) 


	if (addr < __fix_to_virt(FIX_KMAP_END) ||

	    addr > __fix_to_virt(FIX_KMAP_BEGIN)) {

		if (IS_ENABLED(CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP)) {

			/* This _should_ never happen! See above. */

			WARN_ON_ONCE(1);

			return;

		}

		/*

		 * Handle mappings which were obtained by kmap_high_get()

		 * first as the virtual address of such mappings is below