linux-kernel - [PATCH V3 1/3] arm64/mm: Drop __HAVE_ARCH_HUGE_PTEP

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Date:   Fri,  8 May 2020 08:37:49 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-mm@...ck.org, akpm@...ux-foundation.org
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH V3 1/3] arm64/mm: Drop __HAVE_ARCH_HUGE_PTEP_GET

Platform specific huge_ptep_get() is required only when fetching the huge
PTE involves more than just dereferencing the page table pointer. This is
not the case on arm64 platform. Hence huge_ptep_pte() can be dropped along
with it's __HAVE_ARCH_HUGE_PTEP_GET subscription. Before that, it updates
the generic huge_ptep_get() with READ_ONCE() which will prevent known page
table issues with THP on arm64.

https://lore.kernel.org/r/1506527369-19535-1-git-send-email-will.deacon@arm.com/

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
 arch/arm64/include/asm/hugetlb.h | 6 ------
 include/asm-generic/hugetlb.h    | 2 +-
 2 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
index 2eb6c234d594..b88878ddc88b 100644
--- a/arch/arm64/include/asm/hugetlb.h
+++ b/arch/arm64/include/asm/hugetlb.h
@@ -17,12 +17,6 @@
 extern bool arch_hugetlb_migration_supported(struct hstate *h);
 #endif
 
-#define __HAVE_ARCH_HUGE_PTEP_GET
-static inline pte_t huge_ptep_get(pte_t *ptep)
-{
-	return READ_ONCE(*ptep);
-}
-
 static inline int is_hugepage_only_range(struct mm_struct *mm,
 					 unsigned long addr, unsigned long len)
 {
diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h
index 822f433ac95c..40f85decc2ee 100644
--- a/include/asm-generic/hugetlb.h
+++ b/include/asm-generic/hugetlb.h
@@ -122,7 +122,7 @@ static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma,
 #ifndef __HAVE_ARCH_HUGE_PTEP_GET
 static inline pte_t huge_ptep_get(pte_t *ptep)
 {
-	return *ptep;
+	return READ_ONCE(*ptep);
 }
 #endif
 
-- 
2.20.1