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

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Message-Id: <20220127100622.11856-1-hanchuanhua@oppo.com>
Date:   Thu, 27 Jan 2022 18:06:22 +0800
From:   hanchuanhua <hanchuanhua@...o.com>
To:     paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu
Cc:     jszhang@...nel.org, alexandre.ghiti@...onical.com,
        wangkefeng.wang@...wei.com, 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] riscv: mm: Remove the copy operation of pmd

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: hanchuanhua <hanchuanhua@...o.com>
---
 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 4e9efbe..40694f0 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
--
2.7.4

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