linux-kernel - [PATCH v2 3/3] LoongArch: Remove pte buddy set with set_pte and pte

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Message-Id: <20241014035855.1119220-4-maobibo@loongson.cn>
Date: Mon, 14 Oct 2024 11:58:55 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: David Hildenbrand <david@...hat.com>,
	Barry Song <baohua@...nel.org>,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	kasan-dev@...glegroups.com,
	linux-mm@...ck.org
Subject: [PATCH v2 3/3] LoongArch: Remove pte buddy set with set_pte and pte_clear function

For kernel address 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 pte buddy entry.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 arch/loongarch/include/asm/pgtable.h | 35 ++++------------------------
 1 file changed, 5 insertions(+), 30 deletions(-)

diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
index 22e3a8f96213..bc29c95b1710 100644
--- a/arch/loongarch/include/asm/pgtable.h
+++ b/arch/loongarch/include/asm/pgtable.h
@@ -325,40 +325,15 @@ 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 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));
+	pte_t pte;
+
+	pte = ptep_get(ptep);
+	pte_val(pte) &= _PAGE_GLOBAL;
+	set_pte(ptep, pte);
 }
 
 #define PGD_T_LOG2	(__builtin_ffs(sizeof(pgd_t)) - 1)
-- 
2.39.3