drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist

Bugzilla: https://bugzilla.redhat.com/2107713
Upstream status: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
Tested: Ran simple reproducer program. Also ls -l is sufficient to show the reported
sizes.
Conflicts: topology.c changes applied by hand due to not having e795707703b3
("topology/sysfs: export cluster attributes only if an architectures has support").

commit 7ee951acd31a88f941fd6535fbdee3a1567f1d63
Author: Phil Auld pauld@redhat.com
Date: Fri Jul 15 09:49:24 2022 -0400

drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist  

Using bin_attributes with a 0 size causes fstat and friends to return that  
0 size. This breaks userspace code that retrieves the size before reading  
the file. Rather than reverting 75bd50fa841 ("drivers/base/node.c: use  
bin_attribute to break the size limitation of cpumap ABI") let's put in a  
size value at compile time.  

For cpulist the maximum size is on the order of  
        NR_CPUS * (ceil(log10(NR_CPUS)) + 1)/2  

which for 8192 is 20480 (8192 * 5)/2. In order to get near that you'd need  
a system with every other CPU on one node. For example: (0,2,4,8, ... ).  
To simplify the math and support larger NR_CPUS in the future we are using  
(NR_CPUS * 7)/2. We also set it to a min of PAGE_SIZE to retain the older  
behavior for smaller NR_CPUS.  

The cpumap file the size works out to be NR_CPUS/4 + NR_CPUS/32 - 1  
(or NR_CPUS * 9/32 - 1) including the ","s.  

Add a set of macros for these values to cpumask.h so they can be used in  
multiple places. Apply these to the handful of such files in  
drivers/base/topology.c as well as node.c.  

As an example, on an 80 cpu 4-node system (NR_CPUS == 8192):  

before:  

-r--r--r--. 1 root root 0 Jul 12 14:08 system/node/node0/cpulist  
-r--r--r--. 1 root root 0 Jul 11 17:25 system/node/node0/cpumap  

after:  

-r--r--r--. 1 root root 28672 Jul 13 11:32 system/node/node0/cpulist  
-r--r--r--. 1 root root  4096 Jul 13 11:31 system/node/node0/cpumap  

CONFIG_NR_CPUS = 16384  
-r--r--r--. 1 root root 57344 Jul 13 14:03 system/node/node0/cpulist  
-r--r--r--. 1 root root  4607 Jul 13 14:02 system/node/node0/cpumap  

The actual number of cpus doesn't matter for the reported size since they  
are based on NR_CPUS.  

Fixes: 75bd50fa841d ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI")  
Fixes: bb9ec13d156e ("topology: use bin_attribute to break the size limitation of cpumap ABI")  
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>  
Cc: "Rafael J. Wysocki" <rafael@kernel.org>  
Cc: Yury Norov <yury.norov@gmail.com>  
Cc: stable@vger.kernel.org  
Acked-by: Yury Norov <yury.norov@gmail.com> (for include/linux/cpumask.h)  
Signed-off-by: Phil Auld <pauld@redhat.com>  
Link: https://lore.kernel.org/r/20220715134924.3466194-1-pauld@redhat.com  
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>  

Signed-off-by: Phil Auld pauld@redhat.com