linux-kernel - [PATCH v2] MIPS: Do not flush tlb when setting pmd entry

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Message-Id: <1592477815-836-1-git-send-email-maobibo@loongson.cn>
Date:   Thu, 18 Jun 2020 18:56:55 +0800
From:   Bibo Mao <maobibo@...ngson.cn>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Silsby <dansilsby@...il.com>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] MIPS: Do not flush tlb when setting pmd entry

Function set_pmd_at is to set pmd entry, if tlb entry need to
be flushed, there exists pmdp_huge_clear_flush alike function
before set_pmd_at is called. So it is not necessary to call
flush_tlb_all in this function.

In these scenarios, tlb for the pmd range needs to be flushed:
1. privilege degrade such as wrprotect is set on the pmd entry
2. pmd entry is cleared
3. there is exception if set_pmd_at is issued by dup_mmap, since
flush_tlb_mm is called for parent process, it is not necessary
to flush tlb in function copy_huge_pmd.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
v2:
- add the same operation on mips32 system
- update changelog description
---
 arch/mips/mm/pgtable-32.c | 1 -
 arch/mips/mm/pgtable-64.c | 1 -
 2 files changed, 2 deletions(-)

diff --git a/arch/mips/mm/pgtable-32.c b/arch/mips/mm/pgtable-32.c
index bd4b065..61891af 100644
--- a/arch/mips/mm/pgtable-32.c
+++ b/arch/mips/mm/pgtable-32.c
@@ -45,7 +45,6 @@ void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 		pmd_t *pmdp, pmd_t pmd)
 {
 	*pmdp = pmd;
-	flush_tlb_all();
 }
 #endif /* defined(CONFIG_TRANSPARENT_HUGEPAGE) */
 
diff --git a/arch/mips/mm/pgtable-64.c b/arch/mips/mm/pgtable-64.c
index 183ff9f..7536f78 100644
--- a/arch/mips/mm/pgtable-64.c
+++ b/arch/mips/mm/pgtable-64.c
@@ -100,7 +100,6 @@ void set_pmd_at(struct mm_struct *mm, unsigned long addr,
 		pmd_t *pmdp, pmd_t pmd)
 {
 	*pmdp = pmd;
-	flush_tlb_all();
 }
 
 void __init pagetable_init(void)
-- 
1.8.3.1