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>

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 873e363048c6c661eda620bbd4f826ba568c5ba7..116ad654dd593d18a07d68fd61875dd2de614222 100644 (file)
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -456,6 +456,9 @@ 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.