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

[Anju T Sudhakar]

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>
---
 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);
 
-- 
2.7.4