arm64: Do not flush the D-cache for anonymous pages

The D-cache on AArch64 is VIPT non-aliasing, so there is no need to
flush it for anonymous pages.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Will Deacon <will.deacon@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>

arch/arm64/mm/flush.c

@@ -77,14 +77,12 @@ void __flush_dcache_page(struct page *page)
 
 void __sync_icache_dcache(pte_t pte, unsigned long addr)
 {
-	unsigned long pfn;
-	struct page *page;
+	struct page *page = pte_page(pte);
 
-	pfn = pte_pfn(pte);
-	if (!pfn_valid(pfn))
+	/* no flushing needed for anonymous pages */
+	if (!page_mapping(page))
 		return;
 
-	page = pfn_to_page(pfn);
 	if (!test_and_set_bit(PG_dcache_clean, &page->flags)) {
 		__flush_dcache_page(page);
 		__flush_icache_all();

arch/arm64/mm/mmu.c

@@ -339,7 +339,6 @@ void __init paging_init(void)
 	bootmem_init();
 
 	empty_zero_page = virt_to_page(zero_page);
-	__flush_dcache_page(empty_zero_page);
 
 	/*
 	 * TTBR0 is only used for the identity mapping at this stage. Make it