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: <[email protected]> # v3.14+, for older kernels need to drop the 'ishst' Signed-off-by: Will Deacon <[email protected]>
Freescale · Dec 11, 2015 · 32d6397 · 32d6397
1 parent 9cb9c9e
commit 32d6397
Showing 1 changed file with 3 additions and 0 deletions.
diff --git 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.