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

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Date:   Mon, 30 Mar 2020 19:53:19 +0800
From:   Chuanhua Han <hanchuanhua@...hsemi.com>
To:     paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu
Cc:     akpm@...ux-foundation.org, sfr@...b.auug.org.au, peterx@...hat.com,
        shihpo.hung@...ive.com, ebiederm@...ssion.com, schwab@...e.de,
        tglx@...utronix.de, Anup.Patel@....com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Chuanhua Han <hanchuanhua@...hsemi.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: Chuanhua Han <hanchuanhua@...hsemi.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 be84e32adc4c..24f4ebfd2df8 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -208,9 +208,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 vmalloc_fault:
 	{
 		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;
 
@@ -234,12 +234,10 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 			goto no_context;
 		set_pgd(pgd, *pgd_k);
 
-		p4d = p4d_offset(pgd, addr);
 		p4d_k = p4d_offset(pgd_k, addr);
 		if (!p4d_present(*p4d_k))
 			goto no_context;
 
-		pud = pud_offset(p4d, addr);
 		pud_k = pud_offset(p4d_k, addr);
 		if (!pud_present(*pud_k))
 			goto no_context;
@@ -248,11 +246,9 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 		 * 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))
 			goto no_context;
-		set_pmd(pmd, *pmd_k);
 
 		/*
 		 * Make sure the actual PTE exists as well to
-- 
2.17.1