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

[Michael Neuling]

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

> ---
>  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);
>