From: Jeff Hansen <jhansen@cardaccess-inc.com>
Subject: [PATCH] no highpage

On ASUS WL-500gP there are many unexpected "Segmentation fault"s that
seem to be caused by a kernel. They can be avoided by:
1) Disabling highpage
2) Using flush_cache_mm in flush_cache_dup_mm

For details see OpenWrt ticket #2035 https://dev.openwrt.org/ticket/2035
---
--- a/arch/mips/include/asm/page.h
+++ b/arch/mips/include/asm/page.h
@@ -71,6 +71,7 @@ static inline unsigned int page_size_ftl
 #endif /* CONFIG_MIPS_HUGE_TLB_SUPPORT */
 
 #include <linux/pfn.h>
+#include <asm/cpu-features.h>
 
 extern void build_clear_page(void);
 extern void build_copy_page(void);
@@ -110,11 +111,16 @@ static inline void clear_user_page(void
 		flush_data_cache_page((unsigned long)addr);
 }
 
-struct vm_area_struct;
-extern void copy_user_highpage(struct page *to, struct page *from,
-	unsigned long vaddr, struct vm_area_struct *vma);
+static inline void copy_user_page(void *vto, void *vfrom, unsigned long vaddr,
+	struct page *to)
+{
+	extern void (*flush_data_cache_page)(unsigned long addr);
 
-#define __HAVE_ARCH_COPY_USER_HIGHPAGE
+	copy_page(vto, vfrom);
+	if (!cpu_has_ic_fills_f_dc ||
+	    pages_do_alias((unsigned long)vto, vaddr & PAGE_MASK))
+		flush_data_cache_page((unsigned long)vto);
+}
 
 /*
  * These are used to make use of C type-checking..
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -166,30 +166,6 @@ void kunmap_coherent(void)
 	preempt_enable();
 }
 
-void copy_user_highpage(struct page *to, struct page *from,
-	unsigned long vaddr, struct vm_area_struct *vma)
-{
-	void *vfrom, *vto;
-
-	vto = kmap_atomic(to);
-	if (cpu_has_dc_aliases && cpu_use_kmap_coherent &&
-	    page_mapcount(from) && !Page_dcache_dirty(from)) {
-		vfrom = kmap_coherent(from, vaddr);
-		copy_page(vto, vfrom);
-		kunmap_coherent();
-	} else {
-		vfrom = kmap_atomic(from);
-		copy_page(vto, vfrom);
-		kunmap_atomic(vfrom);
-	}
-	if ((!cpu_has_ic_fills_f_dc) ||
-	    pages_do_alias((unsigned long)vto, vaddr & PAGE_MASK))
-		flush_data_cache_page((unsigned long)vto);
-	kunmap_atomic(vto);
-	/* Make sure this page is cleared on other CPU's too before using it */
-	smp_wmb();
-}
-
 void copy_to_user_page(struct vm_area_struct *vma,
 	struct page *page, unsigned long vaddr, void *dst, const void *src,
 	unsigned long len)