linux-kernel - [RFC PATCH v2 10/20] powerpc/mm: Fix __find_linux

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Date: Fri, 17 May 2024 21:00:04 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Jason Gunthorpe <jgg@...dia.com>,
	Peter Xu <peterx@...hat.com>,
	Oscar Salvador <osalvador@...e.de>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: [RFC PATCH v2 10/20] powerpc/mm: Fix __find_linux_pte() on 32 bits with PMD leaf entries

Building on 32 bits with pmd_leaf() not returning always false leads
to the following error:

  CC      arch/powerpc/mm/pgtable.o
arch/powerpc/mm/pgtable.c: In function '__find_linux_pte':
arch/powerpc/mm/pgtable.c:506:1: error: function may return address of local variable [-Werror=return-local-addr]
  506 | }
      | ^
arch/powerpc/mm/pgtable.c:394:15: note: declared here
  394 |         pud_t pud, *pudp;
      |               ^~~
arch/powerpc/mm/pgtable.c:394:15: note: declared here

This is due to pmd_offset() being a no-op in that case.

So rework it for powerpc/32 so that pXd_offset() are used on real
pointers and not on on-stack copies.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/mm/pgtable.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index 59f0d7706d2f..51ee508eeb5b 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -390,8 +390,12 @@ pte_t *__find_linux_pte(pgd_t *pgdir, unsigned long ea,
 			bool *is_thp, unsigned *hpage_shift)
 {
 	pgd_t *pgdp;
-	p4d_t p4d, *p4dp;
-	pud_t pud, *pudp;
+	p4d_t *p4dp;
+	pud_t *pudp;
+#ifdef CONFIG_PPC64
+	p4d_t p4d;
+	pud_t pud;
+#endif
 	pmd_t pmd, *pmdp;
 	pte_t *ret_pte;
 	hugepd_t *hpdp = NULL;
@@ -412,6 +416,7 @@ pte_t *__find_linux_pte(pgd_t *pgdir, unsigned long ea,
 	 */
 	pgdp = pgdir + pgd_index(ea);
 	p4dp = p4d_offset(pgdp, ea);
+#ifdef CONFIG_PPC64
 	p4d  = READ_ONCE(*p4dp);
 	pdshift = P4D_SHIFT;
 
@@ -452,6 +457,11 @@ pte_t *__find_linux_pte(pgd_t *pgdir, unsigned long ea,
 
 	pdshift = PMD_SHIFT;
 	pmdp = pmd_offset(&pud, ea);
+#else
+	p4dp = p4d_offset(pgdp, ea);
+	pudp = pud_offset(p4dp, ea);
+	pmdp = pmd_offset(pudp, ea);
+#endif
 	pmd  = READ_ONCE(*pmdp);
 
 	/*
-- 
2.44.0