linux-kernel - [PATCH 3/3] arm64: mmu: pgd_pgtable

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Date:   Wed, 13 Feb 2019 09:37:38 +0000
From:   Peng Fan <peng.fan@....com>
To:     "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
        "yaojun8558363@...il.com" <yaojun8558363@...il.com>,
        "cpandya@...eaurora.org" <cpandya@...eaurora.org>,
        "robin.murphy@....com" <robin.murphy@....com>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "van.freenix@...il.com" <van.freenix@...il.com>,
        Peng Fan <peng.fan@....com>
Subject: [PATCH 3/3] arm64: mmu: pgd_pgtable_alloc: drop barrier

The barriers are added for empty_zero_page, however the
empty zero page has been moved to bss area by
commit 5227cfa71f9e ("arm64: mm: place empty_zero_page in bss"),
and it alreay added "dsb     ishst" in head.S to make sure
the empty zero page visible to PTW.

pgd_pgtable_alloc is only called by __create_pgd_mapping, and
there are implicit barriers in __create_pgd_mapping, so we
could remove the barrier pgd_pgtable_alloc

Signed-off-by: Peng Fan <peng.fan@....com>
---

Note: this patch tested on qemu-system-aarch64, not real hardware.

 arch/arm64/mm/mmu.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index f61fa7c8fd2e..04e3d4d070ce 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -371,8 +371,6 @@ static phys_addr_t pgd_pgtable_alloc(void)
 	if (!ptr || !pgtable_page_ctor(virt_to_page(ptr)))
 		BUG();
 
-	/* Ensure the zeroed page is visible to the page table walker */
-	dsb(ishst);
 	return __pa(ptr);
 }
 
-- 
2.16.4