target/linux/generic/pending-4.4/101-MIPS-fix-cache-flushing-for-highmem-pages.patch

   1 From: Felix Fietkau <nbd@nbd.name>
   2 Date: Sun, 24 Jan 2016 01:03:51 +0100
   3 Subject: [PATCH] MIPS: fix cache flushing for highmem pages
   4
   5 Most cache flush ops were no-op for highmem pages. This led to nasty
   6 segfaults and (in the case of page_address(page) == NULL) kernel
   7 crashes.
   8
   9 Fix this by always flushing highmem pages using kmap/kunmap_atomic
  10 around the actual cache flush. This might be a bit inefficient, but at
  11 least it's stable.
  12
  13 Signed-off-by: Felix Fietkau <nbd@nbd.name>
  14 ---
  15
  16 --- a/arch/mips/mm/cache.c
  17 +++ b/arch/mips/mm/cache.c
  18 @@ -111,6 +111,13 @@ void __flush_anon_page(struct page *page
  19  {
  20         unsigned long addr = (unsigned long) page_address(page);
  21
  22 +       if (PageHighMem(page)) {
  23 +               addr = (unsigned long)kmap_atomic(page);
  24 +               flush_data_cache_page(addr);
  25 +               __kunmap_atomic((void *)addr);
  26 +               return;
  27 +       }
  28 +
  29         if (pages_do_alias(addr, vmaddr)) {
  30                 if (page_mapped(page) && !Page_dcache_dirty(page)) {
  31                         void *kaddr;