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Message-Id: <1453926929-17663-29-git-send-email-kamal@canonical.com> Date: Wed, 27 Jan 2016 12:31:29 -0800 From: Kamal Mostafa <kamal@...onical.com> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org, kernel-team@...ts.ubuntu.com Cc: Will Deacon <will.deacon@....com>, Kamal Mostafa <kamal@...onical.com> Subject: [PATCH 4.2.y-ckt 028/268] arm64: mm: ensure that the zero page is visible to the page table walker 4.2.8-ckt3 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Will Deacon <will.deacon@....com> commit 32d6397805d00573ce1fa55f408ce2bca15b0ad3 upstream. 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. Signed-off-by: Will Deacon <will.deacon@....com> Signed-off-by: Kamal Mostafa <kamal@...onical.com> --- 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 6a0dc30..3d016b9 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -451,6 +451,9 @@ 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. -- 1.9.1
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