LoongArch: Use static defined zero page rather than allocated

On LoongArch system, there is only one page needed for zero page (no
cache synonyms), and there is no COLOR_ZERO_PAGE, so zero_page_mask is
useless and the macro __HAVE_COLOR_ZERO_PAGE is not necessary.

Like other popular architectures, It is simpler to define the zero page
in kernel BSS code segment rather than dynamically allocate.
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/asm/mmzone.h

@@ -13,6 +13,4 @@ extern struct pglist_data *node_data[];
 
 #define NODE_DATA(nid)	(node_data[(nid)])
 
-extern void setup_zero_pages(void);
-
 #endif /* _ASM_MMZONE_H_ */

arch/loongarch/include/asm/pgtable.h

@@ -70,12 +70,9 @@ struct vm_area_struct;
  * for zero-mapped memory areas etc..
  */
 
-extern unsigned long empty_zero_page;
-extern unsigned long zero_page_mask;
+extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 
-#define ZERO_PAGE(vaddr) \
-	(virt_to_page((void *)(empty_zero_page + (((unsigned long)(vaddr)) & zero_page_mask))))
-#define __HAVE_COLOR_ZERO_PAGE
+#define ZERO_PAGE(vaddr)	virt_to_page(empty_zero_page)
 
 /*
  * TLB refill handlers may also map the vmalloc area into xkvrange.

arch/loongarch/kernel/numa.c

@@ -438,7 +438,6 @@ void __init mem_init(void)
 {
 	high_memory = (void *) __va(get_num_physpages() << PAGE_SHIFT);
 	memblock_free_all();
-	setup_zero_pages();	/* This comes from node 0 */
 }
 
 int pcibus_to_node(struct pci_bus *bus)

arch/loongarch/mm/init.c

@@ -35,33 +35,8 @@
 #include <asm/pgalloc.h>
 #include <asm/tlb.h>
 
-/*
- * We have up to 8 empty zeroed pages so we can map one of the right colour
- * when needed.	 Since page is never written to after the initialization we
- * don't have to care about aliases on other CPUs.
- */
-unsigned long empty_zero_page, zero_page_mask;
+unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
 EXPORT_SYMBOL(empty_zero_page);
-EXPORT_SYMBOL(zero_page_mask);
-
-void setup_zero_pages(void)
-{
-	unsigned int order, i;
-	struct page *page;
-
-	order = 0;
-
-	empty_zero_page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
-	if (!empty_zero_page)
-		panic("Oh boy, that early out of memory?");
-
-	page = virt_to_page((void *)empty_zero_page);
-	split_page(page, order);
-	for (i = 0; i < (1 << order); i++, page++)
-		mark_page_reserved(page);
-
-	zero_page_mask = ((PAGE_SIZE << order) - 1) & PAGE_MASK;
-}
 
 void copy_user_highpage(struct page *to, struct page *from,
 	unsigned long vaddr, struct vm_area_struct *vma)
@@ -106,7 +81,6 @@ void __init mem_init(void)
 	high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
 
 	memblock_free_all();
-	setup_zero_pages();	/* Setup zeroed pages.  */
 }
 #endif /* !CONFIG_NUMA */