linux-kernel - Re: [PATCH v6 14/14] mm: Add basic tests for lazy

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Message-ID: <87a4zhkt6h.ritesh.list@gmail.com>
Date: Wed, 17 Dec 2025 21:16:14 +0530
From: Ritesh Harjani (IBM) <ritesh.list@...il.com>
To: Ryan Roberts <ryan.roberts@....com>, Kevin Brodsky <kevin.brodsky@....com>, Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Alexander Gordeev <agordeev@...ux.ibm.com>, Andreas Larsson <andreas@...sler.com>, 
	Anshuman Khandual <anshuman.khandual@....com>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, 
	Borislav Petkov <bp@...en8.de>, Catalin Marinas <catalin.marinas@....com>, 
	Christophe Leroy <christophe.leroy@...roup.eu>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	David Hildenbrand <david@...hat.com>, "David S. Miller" <davem@...emloft.net>, 
	David Woodhouse <dwmw2@...radead.org>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, 
	Jann Horn <jannh@...gle.com>, Juergen Gross <jgross@...e.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	Madhavan Srinivasan <maddy@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>, Michal Hocko <mhocko@...e.com>, 
	Mike Rapoport <rppt@...nel.org>, Nicholas Piggin <npiggin@...il.com>, 
	Peter Zijlstra <peterz@...radead.org>, Suren Baghdasaryan <surenb@...gle.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Venkat Rao Bagalkote <venkat88@...ux.ibm.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>, Yeoreum Yun <yeoreum.yun@....com>, 
	linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org, 
	sparclinux@...r.kernel.org, xen-devel@...ts.xenproject.org, x86@...nel.org
Subject: Re: [PATCH v6 14/14] mm: Add basic tests for lazy_mmu

Ryan Roberts <ryan.roberts@....com> writes:

> On 17/12/2025 09:26, Kevin Brodsky wrote:
>> On 17/12/2025 05:14, Andrew Morton wrote:
>>> On Mon, 15 Dec 2025 15:03:23 +0000 Kevin Brodsky <kevin.brodsky@....com> wrote:
>>>
>>>> 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.
>>> I needed this for powerpc allmodconfig;
>>>
>>> --- a/arch/powerpc/mm/book3s64/hash_tlb.c~mm-add-basic-tests-for-lazy_mmu-fix
>>> +++ a/arch/powerpc/mm/book3s64/hash_tlb.c
>>> @@ -30,6 +30,7 @@
>>>  #include <trace/events/thp.h>
>>>  
>>>  DEFINE_PER_CPU(struct ppc64_tlb_batch, ppc64_tlb_batch);
>>> +EXPORT_SYMBOL_GPL(ppc64_tlb_batch);
>>>  
>>>  /*
>>>   * A linux PTE was changed and the corresponding hash table entry
>>> @@ -154,6 +155,7 @@ void __flush_tlb_pending(struct ppc64_tl
>>>  		flush_hash_range(i, local);
>>>  	batch->index = 0;
>>>  }
>>> +EXPORT_SYMBOL_GPL(__flush_tlb_pending);
>>>  
>>>  void hash__tlb_flush(struct mmu_gather *tlb)
>>>  {
>>> _
>> 
>> Oh indeed I hadn't considered that arch_{enter,leave}_lazy_mmu_mode()
>> refer to those symbols on powerpc... Maybe a bit overkill to export
>> those just for a test module, but I'm not sure there's a good
>> alternative. Forcing LAZY_MMU_MODE_KUNIT_TEST=y is ugly as it would also
>> force KUNIT=y. Alternatively we could depend on !PPC, not pretty either.
>
> Does EXPORT_SYMBOL_IF_KUNIT() help?
>

yes, that make sense. Thanks for the suggestion!
I guess we will need a diff like this in that case -


diff --git a/arch/powerpc/mm/book3s64/hash_tlb.c b/arch/powerpc/mm/book3s64/hash_tlb.c
index fbdeb8981ae7..ec2941cec815 100644
--- a/arch/powerpc/mm/book3s64/hash_tlb.c
+++ b/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)
 {
diff --git a/mm/tests/lazy_mmu_mode_kunit.c b/mm/tests/lazy_mmu_mode_kunit.c
index 2720eb995714..340d7cda9096 100644
--- a/mm/tests/lazy_mmu_mode_kunit.c
+++ b/mm/tests/lazy_mmu_mode_kunit.c
@@ -69,3 +69,4 @@ kunit_test_suite(lazy_mmu_mode_test_suite);
 
 MODULE_DESCRIPTION("Tests for the lazy MMU mode");
 MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");


-ritesh