[PATCH] drivers/base: cacheinfo: handle absence of caches

[Sudeep Holla]

On some simulators like GEM5, caches may not be simulated. In those
cases, the cache levels and leaves will be zero and will result in
following exception:

Unable to handle kernel NULL pointer dereference at virtual address 0040
pgd = ffffffc0008fa000
[00000040] *pgd=00000009f6807003, *pud=00000009f6807003,
	   *pmd=00000009f6808003, *pte=006000002c010707
Internal error: Oops: 96000005 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.1.0-rc5 #198
task: ffffffc9768a0000 ti: ffffffc9768a8000 task.ti: ffffffc9768a8000
PC is at detect_cache_attributes+0x98/0x2c8
LR is at detect_cache_attributes+0x88/0x2c8

kcalloc(0) returns a special value ZERO_SIZE_PTR which is non-NULL value
but results in fault only on any attempt to dereferencing it. So
checking for the non-NULL pointer will not suffice.

This patch checks for non-zero cache leaf nodes and returns error if
there are no cache leaves in detect_cache_attributes.

Cc: <stable@xxxxxxxxxxxxxxx> # 3.19.x
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Reported-by: William Wang <william.wang@xxxxxxx>
Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
---
 drivers/base/cacheinfo.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index 9c2ba1c97c42..df0c66cb7ad3 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -179,7 +179,7 @@ static int detect_cache_attributes(unsigned int cpu)
 {
 	int ret;

-	if (init_cache_level(cpu))
+	if (init_cache_level(cpu) || !cache_leaves(cpu))
 		return -ENOENT;

 	per_cpu_cacheinfo(cpu) = kcalloc(cache_leaves(cpu),
--
1.9.1

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