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

   1 From: Felix Fietkau <nbd@openwrt.org>
   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@openwrt.org>
  14 ---
  15
  16 --- a/arch/mips/mm/cache.c
  17 +++ b/arch/mips/mm/cache.c
  18 @@ -14,6 +14,7 @@
  19  #include <linux/sched.h>
  20  #include <linux/syscalls.h>
  21  #include <linux/mm.h>
  22 +#include <linux/highmem.h>
  23
  24  #include <asm/cacheflush.h>
  25  #include <asm/processor.h>
  26 @@ -78,18 +79,29 @@ SYSCALL_DEFINE3(cacheflush, unsigned lon
  27         return 0;
  28  }
  29
  30 +static void
  31 +flush_highmem_page(struct page *page)
  32 +{
  33 +       void *addr = kmap_atomic(page);
  34 +       flush_data_cache_page((unsigned long)addr);
  35 +       kunmap_atomic(addr);
  36 +}
  37 +
  38  void __flush_dcache_page(struct page *page)
  39  {
  40         struct address_space *mapping = page_mapping(page);
  41         unsigned long addr;
  42
  43 -       if (PageHighMem(page))
  44 -               return;
  45         if (mapping && !mapping_mapped(mapping)) {
  46                 SetPageDcacheDirty(page);
  47                 return;
  48         }
  49
  50 +       if (PageHighMem(page)) {
  51 +               flush_highmem_page(page);
  52 +               return;
  53 +       }
  54 +
  55         /*
  56          * We could delay the flush for the !page_mapping case too.  But that
  57          * case is for exec env/arg pages and those are %99 certainly going to
  58 @@ -105,6 +117,11 @@ void __flush_anon_page(struct page *page
  59  {
  60         unsigned long addr = (unsigned long) page_address(page);
  61
  62 +       if (PageHighMem(page)) {
  63 +               flush_highmem_page(page);
  64 +               return;
  65 +       }
  66 +
  67         if (pages_do_alias(addr, vmaddr)) {
  68                 if (page_mapped(page) && !Page_dcache_dirty(page)) {
  69                         void *kaddr;
  70 @@ -123,8 +140,10 @@ void __flush_icache_page(struct vm_area_
  71  {
  72         unsigned long addr;
  73
  74 -       if (PageHighMem(page))
  75 +       if (PageHighMem(page)) {
  76 +               flush_highmem_page(page);
  77                 return;
  78 +       }
  79
  80         addr = (unsigned long) page_address(page);
  81         flush_data_cache_page(addr);
  82 @@ -142,12 +161,17 @@ void __update_cache(struct vm_area_struc
  83         if (unlikely(!pfn_valid(pfn)))
  84                 return;
  85         page = pfn_to_page(pfn);
  86 -       if (page_mapping(page) && Page_dcache_dirty(page)) {
  87 +       if (!Page_dcache_dirty(page) || !page_mapping(page))
  88 +               return;
  89 +
  90 +       if (PageHighMem(page)) {
  91 +               flush_highmem_page(page);
  92 +       } else {
  93                 addr = (unsigned long) page_address(page);
  94                 if (exec || pages_do_alias(addr, address & PAGE_MASK))
  95                         flush_data_cache_page(addr);
  96 -               ClearPageDcacheDirty(page);
  97         }
  98 +       ClearPageDcacheDirty(page);
  99  }
 100
 101  unsigned long _page_cachable_default;