mm: add basic tests for lazy_mmu

Add basic KUnit tests for the generic aspects of the lazy MMU mode: ensure
that it appears active when it should, depending on how enable/disable and
pause/resume pairs are nested.

[[email protected]: export ppc64_tlb_batch and __flush_tlb_pending to modules]
[[email protected]: use EXPORT_SYMBOL_IF_KUNIT()]
  Link: https://lkml.kernel.org/r/[email protected]
[[email protected]: move MODULE_IMPORT_NS(), add comment]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kevin Brodsky <[email protected]>
Reviewed-by: Yeoreum Yun <[email protected]>
Signed-off-by: Ritesh Harjani (IBM) <[email protected]>
Acked-by: David Hildenbrand (Red Hat) <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: Andreas Larsson <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Borislav Betkov <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Juegren Gross <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Madhavan Srinivasan <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ritesh Harjani (IBM) <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Thomas Gleinxer <[email protected]>
Cc: Venkat Rao Bagalkote <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

arch/powerpc/mm/book3s64/hash_tlb.c

@@ -25,11 +25,12 @@
 #include <asm/tlb.h>
 #include <asm/bug.h>
 #include <asm/pte-walk.h>
-
+#include <kunit/visibility.h>
 
 #include <trace/events/thp.h>
 
 DEFINE_PER_CPU(struct ppc64_tlb_batch, ppc64_tlb_batch);
+EXPORT_SYMBOL_IF_KUNIT(ppc64_tlb_batch);
 
 /*
  * A linux PTE was changed and the corresponding hash table entry
@@ -154,6 +155,7 @@ void __flush_tlb_pending(struct ppc64_tlb_batch *batch)
 		flush_hash_range(i, local);
 	batch->index = 0;
 }
+EXPORT_SYMBOL_IF_KUNIT(__flush_tlb_pending);
 
 void hash__tlb_flush(struct mmu_gather *tlb)
 {

mm/Kconfig

@@ -1475,6 +1475,18 @@ config ARCH_HAS_LAZY_MMU_MODE
 	  MMU-related architectural state to be deferred until the mode is
 	  exited. See <linux/pgtable.h> for details.
 
+config LAZY_MMU_MODE_KUNIT_TEST
+	tristate "KUnit tests for the lazy MMU mode" if !KUNIT_ALL_TESTS
+	depends on ARCH_HAS_LAZY_MMU_MODE
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  Enable this option to check that the lazy MMU mode interface behaves
+	  as expected. Only tests for the generic interface are included (not
+	  architecture-specific behaviours).
+
+	  If unsure, say N.
+
 source "mm/damon/Kconfig"
 
 endmenu

mm/Makefile

@@ -147,3 +147,4 @@ obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o
 obj-$(CONFIG_EXECMEM) += execmem.o
 obj-$(CONFIG_TMPFS_QUOTA) += shmem_quota.o
 obj-$(CONFIG_PT_RECLAIM) += pt_reclaim.o
+obj-$(CONFIG_LAZY_MMU_MODE_KUNIT_TEST) += tests/lazy_mmu_mode_kunit.o

mm/tests/lazy_mmu_mode_kunit.c

@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <kunit/test.h>
+#include <linux/pgtable.h>
+
+/* For some symbols referenced by arch_{enter,leave}_lazy_mmu_mode on powerpc */
+MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
+
+static void expect_not_active(struct kunit *test)
+{
+	KUNIT_EXPECT_FALSE(test, is_lazy_mmu_mode_active());
+}
+
+static void expect_active(struct kunit *test)
+{
+	KUNIT_EXPECT_TRUE(test, is_lazy_mmu_mode_active());
+}
+
+static void lazy_mmu_mode_active(struct kunit *test)
+{
+	expect_not_active(test);
+
+	lazy_mmu_mode_enable();
+	expect_active(test);
+
+	{
+		/* Nested section */
+		lazy_mmu_mode_enable();
+		expect_active(test);
+
+		lazy_mmu_mode_disable();
+		expect_active(test);
+	}
+
+	{
+		/* Paused section */
+		lazy_mmu_mode_pause();
+		expect_not_active(test);
+
+		{
+			/* No effect (paused) */
+			lazy_mmu_mode_enable();
+			expect_not_active(test);
+
+			lazy_mmu_mode_disable();
+			expect_not_active(test);
+
+			lazy_mmu_mode_pause();
+			expect_not_active(test);
+
+			lazy_mmu_mode_resume();
+			expect_not_active(test);
+		}
+
+		lazy_mmu_mode_resume();
+		expect_active(test);
+	}
+
+	lazy_mmu_mode_disable();
+	expect_not_active(test);
+}
+
+static struct kunit_case lazy_mmu_mode_test_cases[] = {
+	KUNIT_CASE(lazy_mmu_mode_active),
+	{}
+};
+
+static struct kunit_suite lazy_mmu_mode_test_suite = {
+	.name = "lazy_mmu_mode",
+	.test_cases = lazy_mmu_mode_test_cases,
+};
+kunit_test_suite(lazy_mmu_mode_test_suite);
+
+MODULE_DESCRIPTION("Tests for the lazy MMU mode");
+MODULE_LICENSE("GPL");