[PATCH 2/6] arm64: use hw_pte_val for HW PTE atomics

[Muhammad Usama Anjum]

Add hw_pte_val() to preserve an lvalue for the HW PTE bits, so atomic
updates can take their address. pte_val() expects a SW PTE value and
cannot operate directly on a distinct hw_pte_t.

With ARCH_HAS_HW_PTE_T, use pte_val() on the wrapper's __pte member;
otherwise, use pte_val() directly.

The atomic operations and their ordering are unchanged.

Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
---
 arch/arm64/include/asm/pgtable.h | 10 +++++-----
 arch/arm64/mm/fault.c            |  6 +++---
 include/linux/pgtable_types.h    |  4 ++++
 3 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 652ce413be389..4768ec59de555 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1303,7 +1303,7 @@ static inline bool __ptep_test_and_clear_young(struct vm_area_struct *vma,
 	do {
 		old_pte = pte;
 		pte = pte_mkold(pte);
-		pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep),
+		pte_val(pte) = cmpxchg_relaxed(&hw_pte_val(*ptep),
 					       pte_val(old_pte), pte_val(pte));
 	} while (pte_val(pte) != pte_val(old_pte));
 
@@ -1346,7 +1346,7 @@ static inline pte_t __ptep_get_and_clear_anysz(struct mm_struct *mm,
 					       hw_pte_t *ptep,
 					       unsigned long pgsize)
 {
-	pte_t pte = __pte(xchg_relaxed(&pte_val(*ptep), 0));
+	pte_t pte = __pte(xchg_relaxed(&hw_pte_val(*ptep), 0));
 
 	switch (pgsize) {
 	case PAGE_SIZE:
@@ -1422,7 +1422,7 @@ static inline void ___ptep_set_wrprotect(struct mm_struct *mm,
 	do {
 		old_pte = pte;
 		pte = pte_wrprotect(pte);
-		pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep),
+		pte_val(pte) = cmpxchg_relaxed(&hw_pte_val(*ptep),
 					       pte_val(old_pte), pte_val(pte));
 	} while (pte_val(pte) != pte_val(old_pte));
 }
@@ -1460,7 +1460,7 @@ static inline void __clear_young_dirty_pte(struct vm_area_struct *vma,
 		if (flags & CYDP_CLEAR_DIRTY)
 			pte = pte_mkclean(pte);
 
-		pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep),
+		pte_val(pte) = cmpxchg_relaxed(&hw_pte_val(*ptep),
 					       pte_val(old_pte), pte_val(pte));
 	} while (pte_val(pte) != pte_val(old_pte));
 }
@@ -1830,7 +1830,7 @@ static inline bool ptep_try_set(hw_pte_t *ptep, pte_t new_pte)
 {
 	pteval_t old = 0;
 
-	if (!try_cmpxchg(&pte_val(*ptep), &old, pte_val(new_pte)))
+	if (!try_cmpxchg(&hw_pte_val(*ptep), &old, pte_val(new_pte)))
 		return false;
 
 	/*
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index b77f4be88e3ea..7d6c30f27214e 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -225,8 +225,8 @@ int __ptep_set_access_flags_anysz(struct vm_area_struct *vma,
 	/*
 	 * Setting the flags must be done atomically to avoid racing with the
 	 * hardware update of the access/dirty state. The PTE_RDONLY bit must
-	 * be set to the most permissive (lowest value) of *ptep and entry
-	 * (calculated as: a & b == ~(~a | ~b)).
+	 * be set to the most permissive (lowest value) of the current PTE and
+	 * entry (calculated as: a & b == ~(~a | ~b)).
 	 */
 	pte_val(entry) ^= PTE_RDONLY;
 	pteval = pte_val(pte);
@@ -235,7 +235,7 @@ int __ptep_set_access_flags_anysz(struct vm_area_struct *vma,
 		pteval ^= PTE_RDONLY;
 		pteval |= pte_val(entry);
 		pteval ^= PTE_RDONLY;
-		pteval = cmpxchg_relaxed(&pte_val(*ptep), old_pteval, pteval);
+		pteval = cmpxchg_relaxed(&hw_pte_val(*ptep), old_pteval, pteval);
 	} while (pteval != old_pteval);
 
 	/*
diff --git a/include/linux/pgtable_types.h b/include/linux/pgtable_types.h
index d6c5a7548550b..ee4eace5c3e1c 100644
--- a/include/linux/pgtable_types.h
+++ b/include/linux/pgtable_types.h
@@ -9,9 +9,13 @@
 #ifdef CONFIG_ARCH_HAS_HW_PTE_T
 typedef struct __hw_pte_t { pte_t __pte; } hw_pte_t;
 #define __pte_from_hw(pte)	((pte).__pte)
+
+#define hw_pte_val(x)  pte_val((x).__pte)
 #else
 #define hw_pte_t pte_t
 #define __pte_from_hw(pte)	(pte)
+
+#define hw_pte_val(x)  pte_val(x)
 #endif
 
 #endif /* !__ASSEMBLY__ */

-- 
2.47.3