Currently pxxval_set() is defined as WRITE_ONCE() but this will change for
D128 pgtable builds, for which WRITE_ONCE() is not sufficient for single
copy atomicity.

In future this infrastructure can be used for D128 to maintain single copy
atomicity semantics with inline asm blocks.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <redacted>
---
Changes in RFC V2:

- Renamed all ptdesc_ instances as pxxval_ instead

 arch/arm64/include/asm/pgtable.h | 11 ++++++-----
 arch/arm64/mm/mmu.c              |  4 ++--
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 72da582e8d12..c71bb829e9f1 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h

@@ -85,6 +85,7 @@ static inline void arch_leave_lazy_mmu_mode(void)
 }
 
 #define pxxval_get(x)		READ_ONCE(x)
+#define pxxval_set(x, val)	WRITE_ONCE(x, val)

 
 #define pmdp_get pmdp_get
 static inline pmd_t pmdp_get(pmd_t *pmdp)

@@ -385,7 +386,7 @@ static inline pte_t pte_clear_uffd_wp(pte_t pte)
 
 static inline void __set_pte_nosync(pte_t *ptep, pte_t pte)
 {
-	WRITE_ONCE(*ptep, pte);
+	pxxval_set(*ptep, pte);
 }
 
 static inline void __set_pte_complete(pte_t pte)

@@ -856,7 +857,7 @@ static inline void set_pmd(pmd_t *pmdp, pmd_t pmd)
 	}
 #endif /* __PAGETABLE_PMD_FOLDED */
 
-	WRITE_ONCE(*pmdp, pmd);
+	pxxval_set(*pmdp, pmd);
 
 	if (pmd_valid(pmd))
 		queue_pte_barriers();

@@ -921,7 +922,7 @@ static inline void set_pud(pud_t *pudp, pud_t pud)
 		return;
 	}
 
-	WRITE_ONCE(*pudp, pud);
+	pxxval_set(*pudp, pud);
 
 	if (pud_valid(pud))
 		queue_pte_barriers();

@@ -1003,7 +1004,7 @@ static inline void set_p4d(p4d_t *p4dp, p4d_t p4d)
 		return;
 	}
 
-	WRITE_ONCE(*p4dp, p4d);
+	pxxval_set(*p4dp, p4d);
 	queue_pte_barriers();
 }
 

@@ -1131,7 +1132,7 @@ static inline void set_pgd(pgd_t *pgdp, pgd_t pgd)
 		return;
 	}
 
-	WRITE_ONCE(*pgdp, pgd);
+	pxxval_set(*pgdp, pgd);
 	queue_pte_barriers();
 }
 

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 7fbb2ef86cfa..6eb92d8f46be 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c

@@ -76,7 +76,7 @@ void noinstr set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
 	 * writable in the kernel mapping.
 	 */
 	if (rodata_is_rw) {
-		WRITE_ONCE(*pgdp, pgd);
+		pxxval_set(*pgdp, pgd);
 		dsb(ishst);
 		isb();
 		return;

@@ -84,7 +84,7 @@ void noinstr set_swapper_pgd(pgd_t *pgdp, pgd_t pgd)
 
 	spin_lock(&swapper_pgdir_lock);
 	fixmap_pgdp = pgd_set_fixmap(__pa_symbol(pgdp));
-	WRITE_ONCE(*fixmap_pgdp, pgd);
+	pxxval_set(*fixmap_pgdp, pgd);
 	/*
 	 * We need dsb(ishst) here to ensure the page-table-walker sees
 	 * our new entry before set_p?d() returns. The fixmap's