powerpc/mpic: Check if cpu_possible() in mpic_physmask()

[Michael Ellerman]

On Sat, 2018-03-31 at 14:00:24 UTC, Michael Ellerman wrote:
> In mpic_physmask() we loop over all CPUs up to 32, then get the hard
> SMP processor id of that CPU.
> 
> Currently that's possibly walking off the end of the paca array, but
> in a future patch we will change the paca array to be an array of
> pointers, and in that case we will get a NULL for missing CPUs and
> oops. eg:
> 
>   Unable to handle kernel paging request for data at address 0x88888888888888b8
>   Faulting instruction address: 0xc00000000004e380
>   Oops: Kernel access of bad area, sig: 11 [#1]
>   ...
>   NIP .mpic_set_affinity+0x60/0x1a0
>   LR  .irq_do_set_affinity+0x48/0x100
> 
> Fix it by checking the CPU is possible, this also fixes the code if
> there are gaps in the CPU numbering which probably never happens on
> mpic systems but who knows.
> 
> Debugged-by: Nicholas Piggin <npiggin at gmail.com>
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>

Applied to powerpc next.

https://git.kernel.org/powerpc/c/0834d627fbea00c1444075eb3e448e

cheers