On Wed, May 10, 2017 at 1:14 AM, Christoph Hellwig [off-list ref] wrote:

On Wed, May 10, 2017 at 09:08:41AM +0100, Al Viro wrote:

quoted

On Wed, May 10, 2017 at 09:37:04AM +0200, Arnd Bergmann wrote:

quoted

quoted

How about trying to remove all of them?  If we could actually get rid
of all of them, we could drop the arch support, and we'd get faster,
simpler, shorter uaccess code throughout the kernel.

BTW, not all get_user() under KERNEL_DS are plain loads.  There is an
exception - probe_kernel_read().

And various calls that looks like opencoded versions, e.g. drivers/dio
or the ELF loader.

But in the long run we'll just need a separate primitive for that,
but that can wait until the set_fs calls outside the core code are
gone.

I suspect that, on most arches, the primitive is called
__copy_from_user().  We could make the generic code do that except
where overridden.