[PATCH] MIPS: Fix COW D-cache aliasing on fork

Provide a custom copy_user_highpage() to deal with aliasing issues on
MIPS.  It uses kmap_coherent() to map an user page for kernel with same
color.  Rewrite copy_to_user_page() and copy_from_user_page() with the
new interfaces to avoid extra cache flushing.

The main part of this patch was originally written by Ralf Baechle;
Atushi Nemoto did the the debugging.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 25 insertions, 0 deletions

diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index ea2d15370bb7..30245c09d025 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -203,6 +203,31 @@ static inline void kunmap_coherent(struct page *page)
         preempt_check_resched();
 }
 
+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, KM_USER1);
+        if (cpu_has_dc_aliases) {
+                vfrom = kmap_coherent(from, vaddr);
+                copy_page(vto, vfrom);
+                kunmap_coherent(from);
+        } else {
+                vfrom = kmap_atomic(from, KM_USER0);
+                copy_page(vto, vfrom);
+                kunmap_atomic(vfrom, KM_USER0);
+        }
+        if (((vma->vm_flags & VM_EXEC) && !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, KM_USER1);
+        /* Make sure this page is cleared on other CPU's too before using it */
+        smp_wmb();
+}
+
+EXPORT_SYMBOL(copy_user_highpage);
+
 void copy_to_user_page(struct vm_area_struct *vma,
         struct page *page, unsigned long vaddr, void *dst, const void *src,
         unsigned long len)