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[RFC,v3,02/21] ARM: mm: make 2-level pgd_t a scalar

Message ID 20260902-dummy_ptxp3-v3-2-5d8f5b17c25c@arm.com
State New
Headers show
Series mm: change behavior of pXdp_get()/pXd_page() in compile-time folded pgtable | expand

Commit Message

Yeoreum Yun Sept. 2, 2026, 11:56 a.m. UTC 
From: "David Hildenbrand (Arm)" <david@kernel.org>

As pgd_t is returned from a function like pgdp_get(), pgd_t shouldn't
be an array.

So, just use an u64, and extract the right 32bit value in pgd_val().

Leave the STRICT_MM_TYPECHECKS case alone for now.

As an alternative, the STRICT_MM_TYPECHECKS approach could be used here
as well, but using an u64 looks conceptually cleaner, even though
pgd_val() gets a bit more involved.

Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 arch/arm/include/asm/pgtable-2level-types.h | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)
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Patch

diff --git a/arch/arm/include/asm/pgtable-2level-types.h b/arch/arm/include/asm/pgtable-2level-types.h
index 650e793f4142..805044ea315b 100644
--- a/arch/arm/include/asm/pgtable-2level-types.h
+++ b/arch/arm/include/asm/pgtable-2level-types.h
@@ -25,7 +25,7 @@  typedef struct { pteval_t pgprot; } pgprot_t;
 
 #define pte_val(x)      ((x).pte)
 #define pmd_val(x)      ((x).pmd)
-#define pgd_val(x)	((x).pgd[0])
+#define pgd_val(x)      ((x).pgd[0])
 #define pgprot_val(x)   ((x).pgprot)
 
 #define __pte(x)        ((pte_t) { (x) } )
@@ -36,14 +36,28 @@  typedef struct { pteval_t pgprot; } pgprot_t;
 /*
  * .. while these make it easier on the compiler
  */
+typedef u64 pgdval_t;
+
 typedef pteval_t pte_t;
 typedef pmdval_t pmd_t;
-typedef pmdval_t pgd_t[2];
+typedef pgdval_t pgd_t;
 typedef pteval_t pgprot_t;
 
 #define pte_val(x)      (x)
 #define pmd_val(x)      (x)
-#define pgd_val(x)	((x)[0])
+
+static inline pmdval_t pgd_val(pgd_t pgd)
+{
+	/*
+	 * A PGD entry actually corresponds to two PMD entries in the PMD table.
+	 * Both PMD entries point to PTE tables residing in the same physical page,
+	 * but at different offsets. See include/asm/pgtable-2level.h for details.
+	 *
+	 * Historically, pgd_val() has returned the lower of the two PMD entries.
+	 */
+	return (*(pmdval_t (*)[2])&pgd)[0];
+}
+
 #define pgprot_val(x)   (x)
 
 #define __pte(x)        (x)