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.

[akpm@linux-foundation.org: export ppc64_tlb_batch and __flush_tlb_pending to modules]
[ritesh.list@gmail.com: use EXPORT_SYMBOL_IF_KUNIT()]
  Link: https://lkml.kernel.org/r/87a4zhkt6h.ritesh.list@gmail.com
[kevin.brodsky@arm.com: move MODULE_IMPORT_NS(), add comment]
  Link: https://lkml.kernel.org/r/20251217163812.2633648-2-kevin.brodsky@arm.com
Link: https://lkml.kernel.org/r/20251215150323.2218608-15-kevin.brodsky@arm.com
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Juegren Gross <jgross@suse.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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");