x86/cpu/cacheinfo: Fix cache_get_priv_group() for Intel processors

The private pointer provided by the cacheinfo code is used to implement
the AMD L3 cache-specific attributes using a pointer to the northbridge
descriptor. It is needed for performing L3-specific operations and for
that we need a couple of PCI devices and other service information, all
contained in the northbridge descriptor.

This results in failure of cacheinfo setup as shown below as
cache_get_priv_group() returns the uninitialised private attributes which
are not valid for Intel processors.

  ------------[ cut here ]------------
  WARNING: CPU: 3 PID: 1 at fs/sysfs/group.c:102
  internal_create_group+0x151/0x280()
  sysfs: (bin_)attrs not set by subsystem for group: index3/
  Modules linked in:
  CPU: 3 PID: 1 Comm: swapper/0 Not tainted 4.0.0-rc3+ #1
  Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A13 05/11/2014
  ...
  Call Trace:
    dump_stack
    warn_slowpath_common
    warn_slowpath_fmt
    internal_create_group
    sysfs_create_groups
    device_add
    cpu_device_create
    ? __kmalloc
    cache_add_dev
    cacheinfo_sysfs_init
    ? container_dev_init
    do_one_initcall
    kernel_init_freeable
    ? rest_init
    kernel_init
    ret_from_fork
    ? rest_init

This patch fixes the issue by checking if the L3 cache indices are
populated correctly (AMD-specific) before initializing the private
attributes.
Reported-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/intel_cacheinfo.c

@@ -556,7 +556,7 @@ cache_get_priv_group(struct cacheinfo *this_leaf)
 {
 	struct amd_northbridge *nb = this_leaf->priv;
 
-	if (this_leaf->level < 3)
+	if (this_leaf->level < 3 || !nb)
 		return NULL;
 
 	if (nb && nb->l3_cache.indices)