linux-kernel - [PATCH v3] riscv: mm: Remove the copy operation of pmd

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Date:   Thu, 31 Mar 2022 19:29:06 -0700
From:   Chuanhua Han <hanchuanhua@...o.com>
To:     paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu
Cc:     alexandre.ghiti@...onical.com, jszhang@...nel.org,
        mhiramat@...nel.org, akpm@...ux-foundation.org,
        zhengqi.arch@...edance.com, ebiederm@...ssion.com,
        liushixin2@...wei.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, hanchuanhua <hanchuanhua@...o.com>
Subject: [PATCH v3] riscv: mm: Remove the copy operation of pmd

From: hanchuanhua <hanchuanhua@...o.com>

Since all processes share the kernel address space,
we only need to copy pgd in case of a vmalloc page
fault exception, the other levels of page tables are
shared, so the operation of copying pmd is unnecessary.

Signed-off-by: Chuanhua Han <hanchuanhua@...o.com>
---
Changes in v3:
  -Change the real name of signed-off-by.

Changes in v2:
  -Delete incorrect default signatures.

 arch/riscv/mm/fault.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 4e9efbe46d5f..40694f0cab9e 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -102,9 +102,9 @@ static inline void bad_area(struct pt_regs *regs, struct mm_struct *mm, int code
 static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long addr)
 {
 	pgd_t *pgd, *pgd_k;
-	pud_t *pud, *pud_k;
-	p4d_t *p4d, *p4d_k;
-	pmd_t *pmd, *pmd_k;
+	pud_t *pud_k;
+	p4d_t *p4d_k;
+	pmd_t *pmd_k;
 	pte_t *pte_k;
 	int index;
 	unsigned long pfn;
@@ -132,14 +132,12 @@ static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long a
 	}
 	set_pgd(pgd, *pgd_k);
 
-	p4d = p4d_offset(pgd, addr);
 	p4d_k = p4d_offset(pgd_k, addr);
 	if (!p4d_present(*p4d_k)) {
 		no_context(regs, addr);
 		return;
 	}
 
-	pud = pud_offset(p4d, addr);
 	pud_k = pud_offset(p4d_k, addr);
 	if (!pud_present(*pud_k)) {
 		no_context(regs, addr);
@@ -150,13 +148,11 @@ static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long a
 	 * Since the vmalloc area is global, it is unnecessary
 	 * to copy individual PTEs
 	 */
-	pmd = pmd_offset(pud, addr);
 	pmd_k = pmd_offset(pud_k, addr);
 	if (!pmd_present(*pmd_k)) {
 		no_context(regs, addr);
 		return;
 	}
-	set_pmd(pmd, *pmd_k);
 
 	/*
 	 * Make sure the actual PTE exists as well to
-- 
2.25.1