[MIPS] Fix aliasing bug in copy_to_user_page / copy_from_user_page

The current implementation uses a sequence of a cacheflush and a copy.
This is racy in case of a multithreaded debuggee and renders GDB
virtually unusable.

Aside this fixes a performance hog rendering access to /proc/cmdline very
slow and resulting in a enough cache stalls for the 34K AP/SP programming
model to make the bare metal code on the non-Linux VPE miss RT deadlines.

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>

1 files changed, 4 insertions, 15 deletions

diff --git a/include/asm-mips/cacheflush.h b/include/asm-mips/cacheflush.h
index 9ab59e2bb233..e3c9925876a3 100644
--- a/include/asm-mips/cacheflush.h
+++ b/include/asm-mips/cacheflush.h
@@ -55,24 +55,13 @@ extern void (*flush_icache_range)(unsigned long start, unsigned long end);
 #define flush_cache_vmap(start, end)            flush_cache_all()
 #define flush_cache_vunmap(start, end)          flush_cache_all()
 
-static inline void copy_to_user_page(struct vm_area_struct *vma,
+extern void copy_to_user_page(struct vm_area_struct *vma,
         struct page *page, unsigned long vaddr, void *dst, const void *src,
-        unsigned long len)
-{
-        if (cpu_has_dc_aliases)
-                flush_cache_page(vma, vaddr, page_to_pfn(page));
-        memcpy(dst, src, len);
-        __flush_icache_page(vma, page);
-}
+        unsigned long len);
 
-static inline void copy_from_user_page(struct vm_area_struct *vma,
+extern void copy_from_user_page(struct vm_area_struct *vma,
         struct page *page, unsigned long vaddr, void *dst, const void *src,
-        unsigned long len)
-{
-        if (cpu_has_dc_aliases)
-                flush_cache_page(vma, vaddr, page_to_pfn(page));
-        memcpy(dst, src, len);
-}
+        unsigned long len);
 
 extern void (*flush_cache_sigtramp)(unsigned long addr);
 extern void (*flush_icache_all)(void);