s390x help needed - kernel read faults

[Heiko Carstens]

On Mon, Nov 07, 2011 at 06:17:37PM +0100, Mark Wielaard wrote:
> On Mon, Nov 07, 2011 at 10:03:19AM -0600, David Smith wrote:
> > I'm not sure why we provided our own functions, that decision was made a
> > long time ago.  If we can't look at the address and know whether it is a
> > user space or kernel space address, then I don't see much choice than to
> > break up our memory accesses and require the callers to know whether
> > they are accessing kernel space or user space.
> 
> Yes, it seems not that hard to track fully, we mostly do know already.
> The only place where it would be helpful to determine whether or not
> a address is valid for either kernel or user space would be in the
> unwinder. There we walk the stack and stop and/or switch from kernel
> to user stack walking based on whether the PC address is a valid
> kernel or user space address. Is there really no way to tell the
> difference on s390x from kernel space?

If all you have is an address, then no, you cannot tell if it belongs to
user space or kernel space.