On Wed, 2014-07-02 at 17:53 +0200, Stefan Klug wrote:
> Implementation details:
> The patch only touches drivers/usb/core/devio.c.
> In procy_do_submiturb(), it is checked if zerocopy is allowed. This is
> currently a rough
> check which compares the number of required pages to
> ps->dev->bus->sg_tablesize.
It seems to me that the check is per call, so using
multiple calls one could still pin unlimited amounts
of memory.
> I don't know if there is more to check there.
> Then the user memory provided inside the usbdevfs_urb structure is
> pinned to
> physical memory using get_user_pages_fast().
> All the user pages are added to the scatter-gather list and the logic
> continues as before.
How do you enforce the cache coherency rules?
Also you don't have a fall back if get_user_pages_fast()
returns less than requested. It seems to me that than you
ought to fall back buffered IO.
Regards
Oliver
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