[RFC v1 05/10] powerpc/64s: Move serialize_against_pte_lookup() to hash_pgtable.c

Ritesh Harjani (IBM)
2026-02-25T11:05:20Z

Originally,
commit fa4531f753f1 ("powerpc/mm: Don't send IPI to all cpus on THP updates")
introduced serialize_against_pte_lookup() call for both Radix and Hash.

However below commit fixed the race with Radix
commit 70cbc3cc78a9 ("mm: gup: fix the fast GUP race against THP collapse")

And therefore following commit removed the
serialize_against_pte_lookup() call from radix_pgtable.c
commit bedf03416913
("powerpc/64s/radix: don't need to broadcast IPI for radix pmd collapse flush")

Now since serialize_against_pte_lookup() only gets called from
hash__pmdp_collapse_flush(), thus move the related functions to
hash_pgtable.c

Hence this patch:
- moves serialize_against_pte_lookup() from radix_pgtable.c to hash_pgtable.c
- removes the radix specific calls from do_serialize()
- renames do_serialize() to do_nothing().

There should not be any functionality change in this patch.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
arch/powerpc/include/asm/book3s/64/pgtable.h | 1 -
arch/powerpc/mm/book3s64/hash_pgtable.c | 21 ++++++++++++++++
arch/powerpc/mm/book3s64/pgtable.c | 25 --------------------
3 files changed, 21 insertions(+), 26 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 1a91762b455d..ff264d930fe8 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -1400,7 +1400,6 @@ static inline bool arch_needs_pgtable_deposit(void)
return false;
return true;
}
-extern void serialize_against_pte_lookup(struct mm_struct *mm);

#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

diff --git a/arch/powerpc/mm/book3s64/hash_pgtable.c b/arch/powerpc/mm/book3s64/hash_pgtable.c
index ac2a24d15d2e..d9b5b751d7b7 100644
--- a/arch/powerpc/mm/book3s64/hash_pgtable.c
+++ b/arch/powerpc/mm/book3s64/hash_pgtable.c
@@ -221,6 +221,27 @@ unsigned long hash__pmd_hugepage_update(struct mm_struct *mm, unsigned long addr
return old;
}

+static void do_nothing(void *arg)
+{
+
+}
+
+/*
+ * Serialize against __find_linux_pte() which does lock-less
+ * lookup in page tables with local interrupts disabled. For huge pages
+ * it casts pmd_t to pte_t. Since format of pte_t is different from
+ * pmd_t we want to prevent transit from pmd pointing to page table
+ * to pmd pointing to huge page (and back) while interrupts are disabled.
+ * We clear pmd to possibly replace it with page table pointer in
+ * different code paths. So make sure we wait for the parallel
+ * __find_linux_pte() to finish.
+ */
+static void serialize_against_pte_lookup(struct mm_struct *mm)
+{
+ smp_mb();
+ smp_call_function_many(mm_cpumask(mm), do_nothing, mm, 1);
+}
+
pmd_t hash__pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
pmd_t *pmdp)
{
diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s64/pgtable.c
index 359092001670..84284dff650a 100644
--- a/arch/powerpc/mm/book3s64/pgtable.c
+++ b/arch/powerpc/mm/book3s64/pgtable.c
@@ -150,31 +150,6 @@ void set_pud_at(struct mm_struct *mm, unsigned long addr,
return set_pte_at_unchecked(mm, addr, pudp_ptep(pudp), pud_pte(pud));
}

-static void do_serialize(void *arg)
-{
- /* We've taken the IPI, so try to trim the mask while here */
- if (radix_enabled()) {
- struct mm_struct *mm = arg;
- exit_lazy_flush_tlb(mm, false);
- }
-}
-
-/*
- * Serialize against __find_linux_pte() which does lock-less
- * lookup in page tables with local interrupts disabled. For huge pages
- * it casts pmd_t to pte_t. Since format of pte_t is different from
- * pmd_t we want to prevent transit from pmd pointing to page table
- * to pmd pointing to huge page (and back) while interrupts are disabled.
- * We clear pmd to possibly replace it with page table pointer in
- * different code paths. So make sure we wait for the parallel
- * __find_linux_pte() to finish.
- */
-void serialize_against_pte_lookup(struct mm_struct *mm)
-{
- smp_mb();
- smp_call_function_many(mm_cpumask(mm), do_serialize, mm, 1);
-}
-
/*
* We use this to invalidate a pmdp entry before switching from a
* hugepte to regular pmd entry.
--
2.53.0