The author struggles with really basic arithmetic. This test checks for
errors in the helpers that are used to map to and from pcplist indices.

This can be run via a basic kunit.py invocation:

tools/testing/kunit/kunit.py run "page_alloc.*"

That will run it via UML which means no THP or ASI. If you want to test
with those enabled you can set the --arch flag to run it via QEMU:

tools/testing/kunit/kunit.py run --arch=x86_64 \
	--kconfig_add CONFIG_TRANSPARENT_HUGEPAGE=y "page_alloc.*"
tools/testing/kunit/kunit.py run --arch=x86_64 \
	--kconfig_add CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION=y "page_alloc.*"
tools/testing/kunit/kunit.py run --arch=x86_64 \
	--kconfig_add CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION=y \
	--kconfig_add CONFIG_TRANSPARENT_HUGEPAGE=y \
	"page_alloc.*"

Signed-off-by: Brendan Jackman <jackmanb@google.com>

fix
---
 mm/Kconfig           |  5 ++++
 mm/Makefile          |  1 +
 mm/internal.h        |  6 +++++
 mm/page_alloc.c      | 10 +++++---
 mm/page_alloc_test.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 89 insertions(+), 3 deletions(-)

diff --git a/mm/Kconfig b/mm/Kconfig
index 034a1662d8c1af320b2262ebcb0cb51d4622e6b0..e25451c1adbd6e079f2d00e3eb8a28affcedab7e 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1375,4 +1375,9 @@ config FIND_NORMAL_PAGE
 
 source "mm/damon/Kconfig"
 
+config PAGE_ALLOC_KUNIT_TEST
+	tristate "KUnit Tests for page_alloc code" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+
 endmenu
diff --git a/mm/Makefile b/mm/Makefile
index 21abb3353550153a7a477640e4fa6dc6df327541..c6ce46a2abf144f2e62df96ec7f606f90affc5f0 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -65,6 +65,7 @@ page-alloc-$(CONFIG_SHUFFLE_PAGE_ALLOCATOR) += shuffle.o
 memory-hotplug-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
 
 obj-y += page-alloc.o
+obj-$(CONFIG_PAGE_ALLOC_KUNIT_TEST) += page_alloc_test.o
 obj-y += page_frag_cache.o
 obj-y += init-mm.o
 obj-y += memblock.o
diff --git a/mm/internal.h b/mm/internal.h
index 0401412220a76a233e14a7ee7d64c1194fc3759d..6006cfb2b9c7e771a0c647c471901dc7fcdad242 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1693,4 +1693,10 @@ static inline int io_remap_pfn_range_complete(struct vm_area_struct *vma,
 	return remap_pfn_range_complete(vma, addr, pfn, size, prot);
 }
 
+#ifdef CONFIG_KUNIT
+unsigned int order_to_pindex(freetype_t freetype, int order);
+int pindex_to_order(unsigned int pindex);
+bool pcp_allowed_order(unsigned int order);
+#endif /* CONFIG_KUNIT */
+
 #endif	/* __MM_INTERNAL_H */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5943b821089b72fd148bd93ee035c0e70e45ec91..0b205aefd27e188c492c32754db08a4488317bd8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -56,6 +56,7 @@
 #include <linux/cacheinfo.h>
 #include <linux/pgalloc_tag.h>
 #include <asm/div64.h>
+#include <kunit/visibility.h>
 #include "internal.h"
 #include "shuffle.h"
 #include "page_reporting.h"
@@ -691,7 +692,7 @@ static void bad_page(struct page *page, const char *reason)
 	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 }
 
-static inline unsigned int order_to_pindex(freetype_t freetype, int order)
+VISIBLE_IF_KUNIT inline unsigned int order_to_pindex(freetype_t freetype, int order)
 {
 	int migratetype = free_to_migratetype(freetype);
 	/* pindex if the freetype is nonsensitive */
@@ -713,8 +714,9 @@ static inline unsigned int order_to_pindex(freetype_t freetype, int order)
 	return (NR_PCP_LISTS_PER_SENSITIVITY * freetype_sensitive(freetype))
 		+ pindex_ns;
 }
+EXPORT_SYMBOL_IF_KUNIT(order_to_pindex);
 
-inline int pindex_to_order(unsigned int pindex)
+VISIBLE_IF_KUNIT inline int pindex_to_order(unsigned int pindex)
 {
 	/* pindex if the freetype is nonsensitive */
 	int pindex_ns = (pindex % NR_PCP_LISTS_PER_SENSITIVITY);
@@ -731,8 +733,9 @@ inline int pindex_to_order(unsigned int pindex)
 
 	return order;
 }
+EXPORT_SYMBOL_IF_KUNIT(pindex_to_order);
 
-static inline bool pcp_allowed_order(unsigned int order)
+VISIBLE_IF_KUNIT inline bool pcp_allowed_order(unsigned int order)
 {
 	if (order <= PAGE_ALLOC_COSTLY_ORDER)
 		return true;
@@ -742,6 +745,7 @@ static inline bool pcp_allowed_order(unsigned int order)
 #endif
 	return false;
 }
+EXPORT_SYMBOL_IF_KUNIT(pcp_allowed_order);
 
 /*
  * Higher-order pages are called "compound pages".  They are structured thusly:
diff --git a/mm/page_alloc_test.c b/mm/page_alloc_test.c
new file mode 100644
index 0000000000000000000000000000000000000000..1cc615ce90d95c47ecae206a87f2af3fab3a5581
--- /dev/null
+++ b/mm/page_alloc_test.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/bitmap.h>
+
+#include <kunit/test.h>
+
+#include "internal.h"
+
+/* This just checks for basic arithmetic errors. */
+static void test_pindex_helpers(struct kunit *test)
+{
+	unsigned long bitmap[bitmap_size(NR_PCP_LISTS)];
+
+	/* Bit means "pindex not yet used". */
+	bitmap_fill(bitmap, NR_PCP_LISTS);
+
+	for (unsigned int order = 0; order < NR_PAGE_ORDERS; order++) {
+		for (unsigned int mt = 0; mt < MIGRATE_PCPTYPES; mt++)  {
+			if (!pcp_allowed_order(order))
+				continue;
+
+			for (int sensitive = 0; sensitive < NR_SENSITIVITIES; sensitive++) {
+				freetype_t ft = migrate_to_freetype(mt, sensitive);
+				unsigned int pindex = order_to_pindex(ft, order);
+				int got_order;
+
+				KUNIT_ASSERT_LT_MSG(test, pindex, NR_PCP_LISTS,
+					"invalid pindex %d (order %d mt %d sensitive %d)",
+					pindex, order, mt, sensitive);
+				KUNIT_EXPECT_TRUE_MSG(test, test_bit(pindex, bitmap),
+					"pindex %d reused (order %d mt %d sensitive %d)",
+					pindex, order, mt, sensitive);
+
+				/*
+				 * For THP, two migratetypes map to the
+				 * same pindex, just manually exclude one
+				 * of those cases.
+				 */
+				if (!(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
+				      order == HPAGE_PMD_ORDER &&
+				      mt == min(MIGRATE_UNMOVABLE, MIGRATE_RECLAIMABLE)))
+					clear_bit(pindex, bitmap);
+
+				got_order = pindex_to_order(pindex);
+				KUNIT_EXPECT_EQ_MSG(test, order, got_order,
+					"roundtrip failed, got %d want %d (pindex %d mt %d sensitive %d)",
+					got_order, order, pindex, mt, sensitive);
+
+			}
+		}
+	}
+
+	KUNIT_EXPECT_TRUE_MSG(test, bitmap_empty(bitmap, NR_PCP_LISTS),
+		"unused pindices: %*pbl", NR_PCP_LISTS, bitmap);
+}
+
+static struct kunit_case page_alloc_test_cases[] = {
+	KUNIT_CASE(test_pindex_helpers),
+	{}
+};
+
+static struct kunit_suite page_alloc_test_suite = {
+	.name = "page_alloc",
+	.test_cases = page_alloc_test_cases,
+};
+
+kunit_test_suite(page_alloc_test_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");

-- 
2.50.1

Hi Brendan,

kernel test robot noticed the following build errors:

[auto build test ERROR on bf2602a3cb2381fb1a04bf1c39a290518d2538d1]

url:    https://github.com/intel-lab-lkp/linux/commits/Brendan-Jackman/x86-mm-asi-Add-CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION/20250924-230633
base:   bf2602a3cb2381fb1a04bf1c39a290518d2538d1
patch link:    https://lore.kernel.org/r/20250924-b4-asi-page-alloc-v1-13-2d861768041f%40google.com
patch subject: [PATCH 13/21] mm/page_alloc_test: unit test pindex helpers
config: x86_64-buildonly-randconfig-006-20250925 (https://download.01.org/0day-ci/archive/20250925/202509252146.WmdVQlgy-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250925/202509252146.WmdVQlgy-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509252146.WmdVQlgy-lkp@intel.com/

All errors (new ones prefixed by >>):

   mm/page_alloc_test.c: In function 'test_pindex_helpers':
>> mm/page_alloc_test.c:19:30: error: implicit declaration of function 'pcp_allowed_order' [-Wimplicit-function-declaration]
      19 |                         if (!pcp_allowed_order(order))
         |                              ^~~~~~~~~~~~~~~~~
>> mm/page_alloc_test.c:24:55: error: implicit declaration of function 'order_to_pindex' [-Wimplicit-function-declaration]
      24 |                                 unsigned int pindex = order_to_pindex(ft, order);
         |                                                       ^~~~~~~~~~~~~~~
>> mm/page_alloc_test.c:44:45: error: implicit declaration of function 'pindex_to_order'; did you mean 'next_order'? [-Wimplicit-function-declaration]
      44 |                                 got_order = pindex_to_order(pindex);
         |                                             ^~~~~~~~~~~~~~~
         |                                             next_order


vim +/pcp_allowed_order +19 mm/page_alloc_test.c

     8	
     9	/* This just checks for basic arithmetic errors. */
    10	static void test_pindex_helpers(struct kunit *test)
    11	{
    12		unsigned long bitmap[bitmap_size(NR_PCP_LISTS)];
    13	
    14		/* Bit means "pindex not yet used". */
    15		bitmap_fill(bitmap, NR_PCP_LISTS);
    16	
    17		for (unsigned int order = 0; order < NR_PAGE_ORDERS; order++) {
    18			for (unsigned int mt = 0; mt < MIGRATE_PCPTYPES; mt++)  {
  > 19				if (!pcp_allowed_order(order))
    20					continue;
    21	
    22				for (int sensitive = 0; sensitive < NR_SENSITIVITIES; sensitive++) {
    23					freetype_t ft = migrate_to_freetype(mt, sensitive);
  > 24					unsigned int pindex = order_to_pindex(ft, order);
    25					int got_order;
    26	
    27					KUNIT_ASSERT_LT_MSG(test, pindex, NR_PCP_LISTS,
    28						"invalid pindex %d (order %d mt %d sensitive %d)",
    29						pindex, order, mt, sensitive);
    30					KUNIT_EXPECT_TRUE_MSG(test, test_bit(pindex, bitmap),
    31						"pindex %d reused (order %d mt %d sensitive %d)",
    32						pindex, order, mt, sensitive);
    33	
    34					/*
    35					 * For THP, two migratetypes map to the
    36					 * same pindex, just manually exclude one
    37					 * of those cases.
    38					 */
    39					if (!(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
    40					      order == HPAGE_PMD_ORDER &&
    41					      mt == min(MIGRATE_UNMOVABLE, MIGRATE_RECLAIMABLE)))
    42						clear_bit(pindex, bitmap);
    43	
  > 44					got_order = pindex_to_order(pindex);
    45					KUNIT_EXPECT_EQ_MSG(test, order, got_order,
    46						"roundtrip failed, got %d want %d (pindex %d mt %d sensitive %d)",
    47						got_order, order, pindex, mt, sensitive);
    48	
    49				}
    50			}
    51		}
    52	
    53		KUNIT_EXPECT_TRUE_MSG(test, bitmap_empty(bitmap, NR_PCP_LISTS),
    54			"unused pindices: %*pbl", NR_PCP_LISTS, bitmap);
    55	}
    56	

-- 
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https://github.com/intel/lkp-tests/wiki