On 11/30, Roland McGrath wrote: > > Documentation/cachetlb.txt says: > > Any time the kernel writes to a page cache page, _OR_ > the kernel is about to read from a page cache page and > user space shared/writable mappings of this page potentially > exist, this routine is called. > > In your case, the kernel is only reading (write=0 passed to > access_process_vm and get_user_pages). In normal situations, > the page in question will have only a private and read-only > mapping in user space. So the call should not be required in > these cases--if the code can tell that's so. > > Perhaps something like the following would be safe. > But you really need some VM folks to tell you for sure. > > diff --git a/mm/memory.c b/mm/memory.c > index 02e48aa..2864ee7 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1484,7 +1484,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, > pages[i] = page; > > flush_anon_page(vma, page, start); > - flush_dcache_page(page); > + if ((vm_flags & VM_WRITE) || (vma->vm_flags & VM_SHARED) > + flush_dcache_page(page); First of all, I know absolutely nothing about D-cache aliasing. My poor understanding of flush_dcache_page() is: synchronize the kernel/user vision of this memory, in the case when either side can change it. If this is true, then this change doesn't look right in general. Even if (vma->vm_flags & VM_SHARED) == 0, it is possible that tsk can write to this memory, this mapping can be writable and private. Even if we ensure that this mapping is readonly/private, another user-space process can write to this page via shared/writable mapping. I'd like to know if my understanding is correct, I am just curious. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>