powerpc/powernv: Fix oops on P9 DD1 in cause_ipi()

[Michael Ellerman]

On Wed, 2017-04-26 at 10:57:47 UTC, Michael Ellerman wrote:
> Recently we merged the native xive support for Power9, and then separately some
> reworks for doorbell IPI support. In isolation both series were OK, but the
> merged result had a bug in one case.
> 
> On P9 DD1 we use pnv_p9_dd1_cause_ipi() which tries to use doorbells, and then
> falls back to the interrupt controller. However the fallback is implemented by
> calling icp_ops->cause_ipi. But now that xive support is merged we might be
> using xive, in which case icp_ops is not initialised, it's a xics specific
> structure. This leads to an oops such as:
> 
>   Unable to handle kernel paging request for data at address 0x00000028
>   Oops: Kernel access of bad area, sig: 11 [#1]
>   NIP pnv_p9_dd1_cause_ipi+0x74/0xe0
>   LR smp_muxed_ipi_message_pass+0x54/0x70
> 
> To fix it, rather than using icp_ops which might be NULL, have both xics and
> xive set smp_ops->cause_ipi, and then in the powernv code we save that as
> ic_cause_ipi before overriding smp_ops->cause_ipi. For paranoia add a WARN_ON()
> to check if somehow smp_ops->cause_ipi is NULL.
> 
> Fixes: b866cc2199d6 ("powerpc: Change the doorbell IPI calling convention")
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>

Applied to powerpc next.

https://git.kernel.org/powerpc/c/45b21cfeb22087795f0b49397fbe52

cheers