On Thu, Aug 21, 2014 at 03:37:37PM -0400, Peter Feiner wrote:
>
> Thanks Kirill, I prefer your approach. I'll send a v2.
>
> I believe you're right about c9d0bf241451. It seems like passing the old & new
> pgprot through pgprot_modify would handle the problem. Furthermore, as you
> suggest, mprotect_fixup should use pgprot_modify when it turns write
> notification on. I think a patch like this is in order:
>
> Not-signed-off-by: Peter Feiner <pfei...@google.com>
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index c1f2ea4..86f89a1 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1611,18 +1611,15 @@ munmap_back:
> }
>
> if (vma_wants_writenotify(vma)) {
> - pgprot_t pprot = vma->vm_page_prot;
> -
> /* Can vma->vm_page_prot have changed??
> *
> * Answer: Yes, drivers may have changed it in their
> * f_op->mmap method.
> *
> - * Ensures that vmas marked as uncached stay that way.
> + * Ensures that vmas marked with special bits stay that way.
> */
> - vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);
> - if (pgprot_val(pprot) == pgprot_val(pgprot_noncached(pprot)))
> - vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> + vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
> + vm_get_page_prot(vm_flags & ~VM_SHARED);
> }
>
> vma_link(mm, vma, prev, rb_link, rb_parent);
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index c43d557..6826313 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -324,7 +324,8 @@ success:
> vm_get_page_prot(newflags));
>
> if (vma_wants_writenotify(vma)) {
> - vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
> + vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
> + vm_get_page_prot(newflags & ~VM_SHARED));
> dirty_accountable = 1;
> }
Thanks a lot Peter and Kirill for catching it and providing the prelim. fixup.
(Initial
patch doesn't look that right for me because vm-softdirty should involve into
account for newly created/expaned vmas only but not into some deep code such
as fault handlings). Peter does the patch above helps? (out of testing machine
at the moment so cant test myself).
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