Re: [PATCH] mm:D-cache aliasing issue in cow_user_page

[Andrew Morton <akpm@osdl.org>]

On Tue, 17 Oct 2006 13:15:37 +0400
Dmitriy Monakhov <dmonakhov@openvz.org> wrote:

>  from mm/memory.c:
>   1434  static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va)
>   1435  {
>   1436          /*
>   1437           * If the source page was a PFN mapping, we don't have
>   1438           * a "struct page" for it. We do a best-effort copy by
>   1439           * just copying from the original user address. If that
>   1440           * fails, we just zero-fill it. Live with it.
>   1441           */
>   1442          if (unlikely(!src)) {
>   1443                  void *kaddr = kmap_atomic(dst, KM_USER0);
>   1444                  void __user *uaddr = (void __user *)(va & PAGE_MASK);
>   1445  
>   1446                  /*
>   1447                   * This really shouldn't fail, because the page is there
>   1448                   * in the page tables. But it might just be unreadable,
>   1449                   * in which case we just give up and fill the result with
>   1450                   * zeroes.
>   1451                   */
>   1452                  if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
>   1453                          memset(kaddr, 0, PAGE_SIZE);
>   1454                  kunmap_atomic(kaddr, KM_USER0);
>   #### D-cache have to be flushed here.
>   #### It seems it is just forgotten.
> 
>   1455                  return;
>   1456                  
>   1457          }
>   1458          copy_user_highpage(dst, src, va);
>   #### Ok here. flush_dcache_page() called from this func if arch need it 
>   1459  }
> 

This page has just been allocated and is private to the caller - there can
be no userspace mappings of it.