From 32d6397805d00573ce1fa55f408ce2bca15b0ad3 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Thu, 10 Dec 2015 16:05:36 +0000 Subject: [PATCH] arm64: mm: ensure that the zero page is visible to the page table walker In paging_init, we allocate the zero page, memset it to zero and then point TTBR0 to it in order to avoid speculative fetches through the identity mapping. In order to guarantee that the freshly zeroed page is indeed visible to the page table walker, we need to execute a dsb instruction prior to writing the TTBR. Cc: # v3.14+, for older kernels need to drop the 'ishst' Signed-off-by: Will Deacon --- arch/arm64/mm/mmu.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index c04def90f3e4..c5bd5bca8e3d 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -464,6 +464,9 @@ void __init paging_init(void) empty_zero_page = virt_to_page(zero_page); + /* Ensure the zero page is visible to the page table walker */ + dsb(ishst); + /* * TTBR0 is only used for the identity mapping at this stage. Make it * point to zero page to avoid speculatively fetching new entries. -- 2.20.1