[PATCH 4/4] LoongArch: Use atomic operation with set_pte and pte_clear function

[Bibo Mao <maobibo@loongson.cn>]

For kernel space area on LoongArch system, both two consecutive page
table entries should be enabled with PAGE_GLOBAL bit. So with function
set_pte() and pte_clear(), pte buddy entry is checked and set besides
its own pte entry. However it is not atomic operation to set both two
pte entries, there is problem with test_vmalloc test case.

With previous patch, all page table entries are set with PAGE_GLOBAL
bit at beginning. Only its own pte entry need update with function
set_pte() and pte_clear(), nothing to do with buddy pte entry.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
---
 arch/loongarch/include/asm/pgtable.h | 44 ++++++++++------------------
 1 file changed, 15 insertions(+), 29 deletions(-)

diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
index 22e3a8f96213..4be3f0dbecda 100644
--- a/arch/loongarch/include/asm/pgtable.h
+++ b/arch/loongarch/include/asm/pgtable.h
@@ -325,40 +325,26 @@ extern void paging_init(void);
 static inline void set_pte(pte_t *ptep, pte_t pteval)
 {
 	WRITE_ONCE(*ptep, pteval);
+}
 
-	if (pte_val(pteval) & _PAGE_GLOBAL) {
-		pte_t *buddy = ptep_buddy(ptep);
-		/*
-		 * Make sure the buddy is global too (if it's !none,
-		 * it better already be global)
-		 */
-		if (pte_none(ptep_get(buddy))) {
-#ifdef CONFIG_SMP
-			/*
-			 * For SMP, multiple CPUs can race, so we need
-			 * to do this atomically.
-			 */
-			__asm__ __volatile__(
-			__AMOR "$zero, %[global], %[buddy] \n"
-			: [buddy] "+ZB" (buddy->pte)
-			: [global] "r" (_PAGE_GLOBAL)
-			: "memory");
-
-			DBAR(0b11000); /* o_wrw = 0b11000 */
-#else /* !CONFIG_SMP */
-			WRITE_ONCE(*buddy, __pte(pte_val(ptep_get(buddy)) | _PAGE_GLOBAL));
-#endif /* CONFIG_SMP */
-		}
-	}
+static inline unsigned long __ptep_get_and_clear(pte_t *ptep)
+{
+	return atomic64_fetch_and(_PAGE_GLOBAL, (atomic64_t *)&pte_val(*ptep));
 }
 
 static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
 {
-	/* Preserve global status for the pair */
-	if (pte_val(ptep_get(ptep_buddy(ptep))) & _PAGE_GLOBAL)
-		set_pte(ptep, __pte(_PAGE_GLOBAL));
-	else
-		set_pte(ptep, __pte(0));
+	__ptep_get_and_clear(ptep);
+}
+
+#define __HAVE_ARCH_PTEP_GET_AND_CLEAR
+static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
+					unsigned long addr, pte_t *ptep)
+{
+	unsigned long val;
+
+	val = __ptep_get_and_clear(ptep);
+	return __pte(val);
 }
 
 #define PGD_T_LOG2	(__builtin_ffs(sizeof(pgd_t)) - 1)
-- 
2.39.3