Re: [PATCH] mm: extend prefault helpers to fault in more than PAGE_SIZE

[Hillf Danton <dhillf@gmail.com>]

On Thu, Feb 16, 2012 at 11:14 PM, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Thu, Feb 16, 2012 at 09:32:08PM +0800, Hillf Danton wrote:
>> On Thu, Feb 16, 2012 at 8:01 PM, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>> > @@ -416,17 +417,20 @@ static inline int fault_in_pages_writeable(char __user *uaddr, int size)
>> >         * Writing zeroes into userspace here is OK, because we know that if
>> >         * the zero gets there, we'll be overwriting it.
>> >         */
>> > -       ret = __put_user(0, uaddr);
>> > +       while (uaddr <= end) {
>> > +               ret = __put_user(0, uaddr);
>> > +               if (ret != 0)
>> > +                       return ret;
>> > +               uaddr += PAGE_SIZE;
>> > +       }
>>
>> What if
>>              uaddr & ~PAGE_MASK == PAGE_SIZE -3 &&
>>                 end & ~PAGE_MASK == 2
>
> I don't quite follow - can you elaborate upon which issue you're seeing?

I concerned that __put_user(0, end) is missed, but it was added below.

And looks good to me.
Hillf

>        if (ret == 0) {
> -               char __user *end = uaddr + size - 1;
> -
>                /*
>                 * If the page was already mapped, this will get a cache miss
>                 * for sure, so try to avoid doing it.
>                 */
> -               if (((unsigned long)uaddr & PAGE_MASK) !=
> +               if (((unsigned long)uaddr & PAGE_MASK) ==
>                                ((unsigned long)end & PAGE_MASK))
> -                       ret = __put_user(0, end);
> +                       ret = __put_user(0, end);
>        }
>        return ret;