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

[Vasant Hegde]

On 9/1/18 11:10 PM, Mahesh J Salgaonkar 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.
> 
> [  119.306746450,3] Fatal MCE at 000000003002949c   .init_trace_buffers+0x20c
> [  119.306756674,3] CFAR : 0000000030029310
> [  119.306758217,3] SRR0 : 000000003002949c SRR1 : 9000000000201000
> [  119.306760486,3] HSRR0: 000000003000280c HSRR1: 9000000000001000
> [  119.306762704,3] DSISR: 00000040         DAR  : a603087c2000807e
> [  119.306764761,3] LR   : 00000000300294a8 CTR  : 0000000000000000
> [  119.306766796,3] CR   : 40004204         XER  : 00000000
> [  119.306768646,3] GPR00: 00000000300293e0 GPR16: 0000000000000000
> [  119.306770934,3] GPR01: 0000000035d03b90 GPR17: 0000000000000000
> [  119.306773164,3] GPR02: 0000000030123c00 GPR18: 0000000000000000
> [  119.306775430,3] GPR03: 0000000031ce0000 GPR19: 0000000000000000
> [  119.306777662,3] GPR04: 00000000001000a7 GPR20: 0000000000000000
> [  119.306779953,3] GPR05: 0000000000000000 GPR21: 0000000000000000
> [  119.306782111,3] GPR06: 0000000000000000 GPR22: 0000000000000000
> [  119.306784268,3] GPR07: 0000000000000000 GPR23: 00000000001000a7
> [  119.306786455,3] GPR08: 000000000000085f GPR24: 0000000000000077
> [  119.306788681,3] GPR09: a603087c2000804e GPR25: 00000000000fffff
> [  119.306791146,3] GPR10: 00000000a1d9fe4b GPR26: 00000000300c4a4b
> [  119.306793413,3] GPR11: 0000000030099d7c GPR27: 00000000300c4a3a
> [  119.306795599,3] GPR12: 0000000040004202 GPR28: 0000000000101000
> [  119.306797869,3] GPR13: 0000000035d00000 GPR29: 0000200001123000
> [  119.306800179,3] GPR14: 00000000300026b0 GPR30: 0000200001123000
> [  119.306802421,3] GPR15: 0000000000000000 GPR31: 0000000000000000
> 
> Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
> ---
>   core/cpu.c |   17 +++++++++++++++--
>   1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/core/cpu.c b/core/cpu.c
> index 88477f821..8b3e5d995 100644
> --- a/core/cpu.c
> +++ b/core/cpu.c
> @@ -1121,6 +1121,18 @@ void init_cpu_max_pir(void)
>   	prlog(PR_DEBUG, "CPU: New max PIR set to 0x%x\n", cpu_max_pir);
>   }
> 
> +static void init_all_cpu_threads(void)
> +{
> +	unsigned int pir;
> +	struct cpu_thread *t;
> +
> +	for (pir = 0; pir <= cpu_max_pir; pir++) {
> +		t = &cpu_stacks[pir].cpu;
> +		if (t != boot_cpu)
> +			init_cpu_thread(t, cpu_state_no_cpu, pir);

If CPU is not present we should just clear that memory. I don't think we should 
init those CPUs which are not present.

-Vasant