Messages in this thread |  | | | Date | Wed, 01 Dec 2010 18:10:12 +0100 | | From | Michal Simek <> | | Subject | Re: Flushing whole page instead of work for ptrace |
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Roland McGrath wrote: > This is a VM question more than a ptrace question. > I can't give you any authoritative answers about the VM issues. > > 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); > } > if (vmas) > vmas[i] = vma; > > > Thanks, > Roland
Andrew any comment?
Thanks, Michal
-- Michal Simek, Ing. (M.Eng) PetaLogix - Linux Solutions for a Reconfigurable World w: www.petalogix.com p: +61-7-30090663,+42-0-721842854 f: +61-7-30090663
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