[PATCH] powerpc/perf: Fix memory allocation for core-imc based on num_possible_cpus()

[Madhavan Srinivasan]

On Saturday 12 May 2018 05:15 AM, Michael Neuling wrote:
> On Fri, 2018-05-11 at 19:13 +0530, Anju T Sudhakar wrote:
>> Currently memory is allocated for core-imc based on cpu_present_mask, which
>> has
>> bit 'cpu' set iff cpu is populated. We use  (cpu number / threads per core)
>> as as array index to access the memory.
>> So in a system with guarded cores, since allocation happens based on
>> cpu_present_mask, (cpu number / threads per core) bounds the index and leads
>> to memory overflow.
>>
>> The issue is exposed in a guard test.
>> The guard test will make some CPU's as un-available to the system during boot
>> time as well as at runtime. So when the cpu is unavailable to the system
>> during
>> boot time, the memory allocation happens depending on the number of available
>> cpus. And when we access the memory using (cpu number / threads per core) as
>> the
>> index the system crashes due to memory overflow.
>>
>> Allocating memory for core-imc based on cpu_possible_mask, which has
>> bit 'cpu' set iff cpu is populatable, will fix this issue.
>>
>> Reported-by: Pridhiviraj Paidipeddi <ppaidipe at linux.vnet.ibm.com>
>> Signed-off-by: Anju T Sudhakar <anju at linux.vnet.ibm.com>
> Thanks, this should be:
>
> Cc: <stable at vger.kernel.org> # 4.14

Thanks for marking to stable. But it should go to 4.14+ stable releases.

Maddy

>> ---
>>   arch/powerpc/perf/imc-pmu.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
>> index d7532e7..75fb23c 100644
>> --- a/arch/powerpc/perf/imc-pmu.c
>> +++ b/arch/powerpc/perf/imc-pmu.c
>> @@ -1146,7 +1146,7 @@ static int init_nest_pmu_ref(void)
>>   
>>   static void cleanup_all_core_imc_memory(void)
>>   {
>> -	int i, nr_cores = DIV_ROUND_UP(num_present_cpus(), threads_per_core);
>> +	int i, nr_cores = DIV_ROUND_UP(num_possible_cpus(),
>> threads_per_core);
>>   	struct imc_mem_info *ptr = core_imc_pmu->mem_info;
>>   	int size = core_imc_pmu->counter_mem_size;
>>   
>> @@ -1264,7 +1264,7 @@ static int imc_mem_init(struct imc_pmu *pmu_ptr, struct
>> device_node *parent,
>>   		if (!pmu_ptr->pmu.name)
>>   			return -ENOMEM;
>>   
>> -		nr_cores = DIV_ROUND_UP(num_present_cpus(),
>> threads_per_core);
>> +		nr_cores = DIV_ROUND_UP(num_possible_cpus(),
>> threads_per_core);
>>   		pmu_ptr->mem_info = kcalloc(nr_cores, sizeof(struct
>> imc_mem_info),
>>   								GFP_KERNEL);
>>