target/linux/generic/pending-4.19/100-MIPS-fix-cache-flushing-for-highmem-pages.patch

   1 From: Felix Fietkau <nbd@nbd.name>
   2 Subject: MIPS: fix cache flushing for highmem pages
   3
   4 Most cache flush ops were no-op for highmem pages. This led to nasty
   5 segfaults and (in the case of page_address(page) == NULL) kernel
   6 crashes.
   7
   8 Fix this by always flushing highmem pages using kmap/kunmap_atomic
   9 around the actual cache flush. This might be a bit inefficient, but at
  10 least it's stable.
  11
  12 Signed-off-by: Felix Fietkau <nbd@nbd.name>
  13 ---
  14
  15 --- a/arch/mips/mm/cache.c
  16 +++ b/arch/mips/mm/cache.c
  17 @@ -116,6 +116,13 @@ void __flush_anon_page(struct page *page
  18  {
  19         unsigned long addr = (unsigned long) page_address(page);
  20
  21 +       if (PageHighMem(page)) {
  22 +               addr = (unsigned long)kmap_atomic(page);
  23 +               flush_data_cache_page(addr);
  24 +               __kunmap_atomic((void *)addr);
  25 +               return;
  26 +       }
  27 +
  28         if (pages_do_alias(addr, vmaddr)) {
  29                 if (page_mapcount(page) && !Page_dcache_dirty(page)) {
  30                         void *kaddr;