linux-kernel - [PATCH v3 3/3] mm/memory.c: Add memory read privilege before filling PTE entry

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Message-Id: <1589778529-25627-3-git-send-email-maobibo@loongson.cn>
Date:   Mon, 18 May 2020 13:08:49 +0800
From:   Bibo Mao <maobibo@...ngson.cn>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Huacai Chen <chenhc@...ote.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul Burton <paulburton@...nel.org>,
        Dmitry Korotin <dkorotin@...ecomp.com>,
        Philippe Mathieu-Daudé <f4bug@...at.org>,
        Stafford Horne <shorne@...il.com>,
        Steven Price <steven.price@....com>,
        Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        "Maciej W. Rozycki" <macro@....com>, linux-mm@...ck.org,
        David Hildenbrand <david@...hat.com>
Subject: [PATCH v3 3/3] mm/memory.c: Add memory read privilege before filling PTE entry

On mips platform, hw PTE entry valid bit is set in pte_mkyoung
function, it is used to set physical page with readable privilege.

Here add pte_mkyoung function to make page readable on MIPS platform
during page fault handling. This patch improves page fault latency
about 10% on my MIPS machine with lmbench lat_pagefault case.

Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
 mm/memory.c   | 3 +++
 mm/mprotect.c | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index 2eb59a9..2399dcb 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2704,6 +2704,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 		}
 		flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
 		entry = mk_pte(new_page, vma->vm_page_prot);
+		entry = pte_mkyoung(entry);
 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 		/*
 		 * Clear the pte entry and flush it first, before updating the
@@ -3378,6 +3379,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 	__SetPageUptodate(page);
 
 	entry = mk_pte(page, vma->vm_page_prot);
+	entry = pte_mkyoung(entry);
 	if (vma->vm_flags & VM_WRITE)
 		entry = pte_mkwrite(pte_mkdirty(entry));
 
@@ -3660,6 +3662,7 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
 
 	flush_icache_page(vma, page);
 	entry = mk_pte(page, vma->vm_page_prot);
+	entry = pte_mkyoung(entry);
 	if (write)
 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 	/* copy-on-write page */
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 494192ca..673f1cd 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -131,6 +131,8 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 				ptent = pte_clear_uffd_wp(ptent);
 			}
 
+			if (vma->vm_flags & VM_READ)
+				ptent = pte_mkyoung(ptent);
 			/* Avoid taking write faults for known dirty pages */
 			if (dirty_accountable && pte_dirty(ptent) &&
 					(pte_soft_dirty(ptent) ||
-- 
1.8.3.1