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arm64: mm: ensure that the zero page is visible to the page table walker 

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@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Will Deacon 2015-12-10 16:05:36 +00:00 committed by Greg Kroah-Hartman
parent c2db3a421b
commit c8f487a49a
1 changed files with 3 additions and 0 deletions
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arch/arm64/mm/mmu.c
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@ -348,6 +348,9 @@ 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();
/*
* TTBR0 is only used for the identity mapping at this stage. Make it
* point to zero page to avoid speculatively fetching new entries.