[Skiboot] [PATCH] core/cpu: Initialize all cpu thread areas to avoid invalid memory access.

[Mahesh Jagannath Salgaonkar]

On 09/03/2018 11:20 AM, Oliver wrote:
> On Sun, Sep 2, 2018 at 3:40 AM, Mahesh J Salgaonkar
> <mahesh at linux.vnet.ibm.com> wrote:
>> From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
>>
>> Currently we initialize cpu stack memory only for cpu pir that is found on
>> the device-tree. For the rest, the cpu thread contents are uninitialized.
>> This sometime causes for_each_cpu* macros to return cpu thread for pir/cpu
>> which isn't present on the system. The for_each_cpu* macros iterate over
>> cpu stacks using pir as index and returns cpu thread pointer if
>> state != cpu_state_no_cpu. For cpus that are not found on device-tree the
>> state may hold junk value leading opal to access invalid cpu thread area.
>> This further leads to accessing pointers with junk values causing machine
>> check (MCE) during OPAL init code. Fix this by Initializing all the cpu
>> thread areas upto cpu_max_pir.
> 
> Is this from a cold IPL or MPIPL? Memory should be zeroed before we
> enter OPAL so if there is junk in the stack area we might have a data
> corruption problem,

This is happening during re-IPL (OS reboot). On FSP, per Dean Sanner, OS
reboot requests get transformed into an MPIPL. On cold IPL the memory is
all zeroed and we don't see this issue during first IPL.

> 
> Reviewed-by: Oliver O'Halloran <oohall at gmail.com>