[v5] drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist

[PATCH v5] drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist

Posted by Phil Auld 3 years, 9 months ago

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: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI")
Fixes: bb9ec13d156 ("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
Signed-off-by: Phil Auld <pauld@redhat.com>
---
v2: Fix cpumap size calculation. Increase multiplier for cpulist size.

v3: Add comments in code.

v4: Define constants in cpumask.h. Move comments there. Also fix
topology.c.

v5: Fixed math based on Yury's corrections.

 drivers/base/node.c     |  4 ++--
 drivers/base/topology.c | 32 ++++++++++++++++----------------
 include/linux/cpumask.h | 18 ++++++++++++++++++
 3 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 0ac6376ef7a1..eb0f43784c2b 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -45,7 +45,7 @@ static inline ssize_t cpumap_read(struct file *file, struct kobject *kobj,
 	return n;
 }
 
-static BIN_ATTR_RO(cpumap, 0);
+static BIN_ATTR_RO(cpumap, CPUMAP_FILE_MAX_BYTES);
 
 static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
 				   struct bin_attribute *attr, char *buf,
@@ -66,7 +66,7 @@ static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
 	return n;
 }
 
-static BIN_ATTR_RO(cpulist, 0);
+static BIN_ATTR_RO(cpulist, CPULIST_FILE_MAX_BYTES);
 
 /**
  * struct node_access_nodes - Access class device to hold user visible
diff --git a/drivers/base/topology.c b/drivers/base/topology.c
index ac6ad9ab67f9..89f98be5c5b9 100644
--- a/drivers/base/topology.c
+++ b/drivers/base/topology.c
@@ -62,47 +62,47 @@ define_id_show_func(ppin, "0x%llx");
 static DEVICE_ATTR_ADMIN_RO(ppin);
 
 define_siblings_read_func(thread_siblings, sibling_cpumask);
-static BIN_ATTR_RO(thread_siblings, 0);
-static BIN_ATTR_RO(thread_siblings_list, 0);
+static BIN_ATTR_RO(thread_siblings, CPUMAP_FILE_MAX_BYTES);
+static BIN_ATTR_RO(thread_siblings_list, CPULIST_FILE_MAX_BYTES);
 
 define_siblings_read_func(core_cpus, sibling_cpumask);
-static BIN_ATTR_RO(core_cpus, 0);
-static BIN_ATTR_RO(core_cpus_list, 0);
+static BIN_ATTR_RO(core_cpus, CPUMAP_FILE_MAX_BYTES);
+static BIN_ATTR_RO(core_cpus_list, CPULIST_FILE_MAX_BYTES);
 
 define_siblings_read_func(core_siblings, core_cpumask);
-static BIN_ATTR_RO(core_siblings, 0);
-static BIN_ATTR_RO(core_siblings_list, 0);
+static BIN_ATTR_RO(core_siblings, CPUMAP_FILE_MAX_BYTES);
+static BIN_ATTR_RO(core_siblings_list, CPULIST_FILE_MAX_BYTES);
 
 #ifdef TOPOLOGY_CLUSTER_SYSFS
 define_siblings_read_func(cluster_cpus, cluster_cpumask);
-static BIN_ATTR_RO(cluster_cpus, 0);
-static BIN_ATTR_RO(cluster_cpus_list, 0);
+static BIN_ATTR_RO(cluster_cpus, CPUMAP_FILE_MAX_BYTES);
+static BIN_ATTR_RO(cluster_cpus_list, CPULIST_FILE_MAX_BYTES);
 #endif
 
 #ifdef TOPOLOGY_DIE_SYSFS
 define_siblings_read_func(die_cpus, die_cpumask);
-static BIN_ATTR_RO(die_cpus, 0);
-static BIN_ATTR_RO(die_cpus_list, 0);
+static BIN_ATTR_RO(die_cpus, CPUMAP_FILE_MAX_BYTES);
+static BIN_ATTR_RO(die_cpus_list, CPULIST_FILE_MAX_BYTES);
 #endif
 
 define_siblings_read_func(package_cpus, core_cpumask);
-static BIN_ATTR_RO(package_cpus, 0);
-static BIN_ATTR_RO(package_cpus_list, 0);
+static BIN_ATTR_RO(package_cpus, CPUMAP_FILE_MAX_BYTES);
+static BIN_ATTR_RO(package_cpus_list, CPULIST_FILE_MAX_BYTES);
 
 #ifdef TOPOLOGY_BOOK_SYSFS
 define_id_show_func(book_id, "%d");
 static DEVICE_ATTR_RO(book_id);
 define_siblings_read_func(book_siblings, book_cpumask);
-static BIN_ATTR_RO(book_siblings, 0);
-static BIN_ATTR_RO(book_siblings_list, 0);
+static BIN_ATTR_RO(book_siblings, CPUMAP_FILE_MAX_BYTES);
+static BIN_ATTR_RO(book_siblings_list, CPULIST_FILE_MAX_BYTES);
 #endif
 
 #ifdef TOPOLOGY_DRAWER_SYSFS
 define_id_show_func(drawer_id, "%d");
 static DEVICE_ATTR_RO(drawer_id);
 define_siblings_read_func(drawer_siblings, drawer_cpumask);
-static BIN_ATTR_RO(drawer_siblings, 0);
-static BIN_ATTR_RO(drawer_siblings_list, 0);
+static BIN_ATTR_RO(drawer_siblings, CPUMAP_FILE_MAX_BYTES);
+static BIN_ATTR_RO(drawer_siblings_list, CPULIST_FILE_MAX_BYTES);
 #endif
 
 static struct bin_attribute *bin_attrs[] = {
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index fe29ac7cc469..4592d0845941 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -1071,4 +1071,22 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
 	[0] =  1UL							\
 } }
 
+/*
+ * Provide a valid theoretical max size for cpumap and cpulist sysfs files
+ * to avoid breaking userspace which may allocate a buffer based on the size
+ * reported by e.g. fstat.
+ *
+ * for cpumap NR_CPUS * 9/32 - 1 should be an exact length.
+ *
+ * For cpulist 7 is (ceil(log10(NR_CPUS)) + 1) allowing for NR_CPUS to be up
+ * to 2 orders of magnitude larger than 8192. And then we divide by 2 to
+ * cover a worst-case of every other cpu being on one of two nodes for a
+ * very large NR_CPUS.
+ *
+ *  Use PAGE_SIZE as a minimum for smaller configurations.
+ */
+#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \
+					? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE)
+#define CPULIST_FILE_MAX_BYTES  (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE)
+
 #endif /* __LINUX_CPUMASK_H */
-- 
2.31.1

Re: [PATCH v5] drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist

Posted by Greg Kroah-Hartman 3 years, 9 months ago

On Fri, Jul 15, 2022 at 09:49:24AM -0400, Phil Auld wrote:
> 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: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI")
> Fixes: bb9ec13d156 ("topology: use bin_attribute to break the size limitation of cpumap ABI")

Nit, use the full 12 characters otherwise our tools will complain.  I'll
go fix it up by hand...

thanks for sticking with this.

greg k-h

Re: [PATCH v5] drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist

Posted by Phil Auld 3 years, 9 months ago

On Fri, Jul 15, 2022 at 05:37:13PM +0200 Greg Kroah-Hartman wrote:
> On Fri, Jul 15, 2022 at 09:49:24AM -0400, Phil Auld wrote:
> > 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: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI")
> > Fixes: bb9ec13d156 ("topology: use bin_attribute to break the size limitation of cpumap ABI")
> 
> Nit, use the full 12 characters otherwise our tools will complain.  I'll
> go fix it up by hand...
>

Erm, counting is hard...  I thought I did have 12 :)

> thanks for sticking with this.

Thanks for the patience.


Cheers,
Phil

> 
> greg k-h
> 

--

Re: [PATCH v5] drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist

Posted by Yury Norov 3 years, 9 months ago

On Fri, Jul 15, 2022 at 09:49:24AM -0400, Phil Auld wrote:
> 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: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI")
> Fixes: bb9ec13d156 ("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
> Signed-off-by: Phil Auld <pauld@redhat.com>

Acked-by: Yury Norov <yury.norov@gmail.com> (for include/linux/cpumask.h)

> ---
> v2: Fix cpumap size calculation. Increase multiplier for cpulist size.
> 
> v3: Add comments in code.
> 
> v4: Define constants in cpumask.h. Move comments there. Also fix
> topology.c.
> 
> v5: Fixed math based on Yury's corrections.
> 
>  drivers/base/node.c     |  4 ++--
>  drivers/base/topology.c | 32 ++++++++++++++++----------------
>  include/linux/cpumask.h | 18 ++++++++++++++++++
>  3 files changed, 36 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 0ac6376ef7a1..eb0f43784c2b 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -45,7 +45,7 @@ static inline ssize_t cpumap_read(struct file *file, struct kobject *kobj,
>  	return n;
>  }
>  
> -static BIN_ATTR_RO(cpumap, 0);
> +static BIN_ATTR_RO(cpumap, CPUMAP_FILE_MAX_BYTES);
>  
>  static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
>  				   struct bin_attribute *attr, char *buf,
> @@ -66,7 +66,7 @@ static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
>  	return n;
>  }
>  
> -static BIN_ATTR_RO(cpulist, 0);
> +static BIN_ATTR_RO(cpulist, CPULIST_FILE_MAX_BYTES);
>  
>  /**
>   * struct node_access_nodes - Access class device to hold user visible
> diff --git a/drivers/base/topology.c b/drivers/base/topology.c
> index ac6ad9ab67f9..89f98be5c5b9 100644
> --- a/drivers/base/topology.c
> +++ b/drivers/base/topology.c
> @@ -62,47 +62,47 @@ define_id_show_func(ppin, "0x%llx");
>  static DEVICE_ATTR_ADMIN_RO(ppin);
>  
>  define_siblings_read_func(thread_siblings, sibling_cpumask);
> -static BIN_ATTR_RO(thread_siblings, 0);
> -static BIN_ATTR_RO(thread_siblings_list, 0);
> +static BIN_ATTR_RO(thread_siblings, CPUMAP_FILE_MAX_BYTES);
> +static BIN_ATTR_RO(thread_siblings_list, CPULIST_FILE_MAX_BYTES);
>  
>  define_siblings_read_func(core_cpus, sibling_cpumask);
> -static BIN_ATTR_RO(core_cpus, 0);
> -static BIN_ATTR_RO(core_cpus_list, 0);
> +static BIN_ATTR_RO(core_cpus, CPUMAP_FILE_MAX_BYTES);
> +static BIN_ATTR_RO(core_cpus_list, CPULIST_FILE_MAX_BYTES);
>  
>  define_siblings_read_func(core_siblings, core_cpumask);
> -static BIN_ATTR_RO(core_siblings, 0);
> -static BIN_ATTR_RO(core_siblings_list, 0);
> +static BIN_ATTR_RO(core_siblings, CPUMAP_FILE_MAX_BYTES);
> +static BIN_ATTR_RO(core_siblings_list, CPULIST_FILE_MAX_BYTES);
>  
>  #ifdef TOPOLOGY_CLUSTER_SYSFS
>  define_siblings_read_func(cluster_cpus, cluster_cpumask);
> -static BIN_ATTR_RO(cluster_cpus, 0);
> -static BIN_ATTR_RO(cluster_cpus_list, 0);
> +static BIN_ATTR_RO(cluster_cpus, CPUMAP_FILE_MAX_BYTES);
> +static BIN_ATTR_RO(cluster_cpus_list, CPULIST_FILE_MAX_BYTES);
>  #endif
>  
>  #ifdef TOPOLOGY_DIE_SYSFS
>  define_siblings_read_func(die_cpus, die_cpumask);
> -static BIN_ATTR_RO(die_cpus, 0);
> -static BIN_ATTR_RO(die_cpus_list, 0);
> +static BIN_ATTR_RO(die_cpus, CPUMAP_FILE_MAX_BYTES);
> +static BIN_ATTR_RO(die_cpus_list, CPULIST_FILE_MAX_BYTES);
>  #endif
>  
>  define_siblings_read_func(package_cpus, core_cpumask);
> -static BIN_ATTR_RO(package_cpus, 0);
> -static BIN_ATTR_RO(package_cpus_list, 0);
> +static BIN_ATTR_RO(package_cpus, CPUMAP_FILE_MAX_BYTES);
> +static BIN_ATTR_RO(package_cpus_list, CPULIST_FILE_MAX_BYTES);
>  
>  #ifdef TOPOLOGY_BOOK_SYSFS
>  define_id_show_func(book_id, "%d");
>  static DEVICE_ATTR_RO(book_id);
>  define_siblings_read_func(book_siblings, book_cpumask);
> -static BIN_ATTR_RO(book_siblings, 0);
> -static BIN_ATTR_RO(book_siblings_list, 0);
> +static BIN_ATTR_RO(book_siblings, CPUMAP_FILE_MAX_BYTES);
> +static BIN_ATTR_RO(book_siblings_list, CPULIST_FILE_MAX_BYTES);
>  #endif
>  
>  #ifdef TOPOLOGY_DRAWER_SYSFS
>  define_id_show_func(drawer_id, "%d");
>  static DEVICE_ATTR_RO(drawer_id);
>  define_siblings_read_func(drawer_siblings, drawer_cpumask);
> -static BIN_ATTR_RO(drawer_siblings, 0);
> -static BIN_ATTR_RO(drawer_siblings_list, 0);
> +static BIN_ATTR_RO(drawer_siblings, CPUMAP_FILE_MAX_BYTES);
> +static BIN_ATTR_RO(drawer_siblings_list, CPULIST_FILE_MAX_BYTES);
>  #endif
>  
>  static struct bin_attribute *bin_attrs[] = {
> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> index fe29ac7cc469..4592d0845941 100644
> --- a/include/linux/cpumask.h
> +++ b/include/linux/cpumask.h
> @@ -1071,4 +1071,22 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
>  	[0] =  1UL							\
>  } }
>  
> +/*
> + * Provide a valid theoretical max size for cpumap and cpulist sysfs files
> + * to avoid breaking userspace which may allocate a buffer based on the size
> + * reported by e.g. fstat.
> + *
> + * for cpumap NR_CPUS * 9/32 - 1 should be an exact length.
> + *
> + * For cpulist 7 is (ceil(log10(NR_CPUS)) + 1) allowing for NR_CPUS to be up
> + * to 2 orders of magnitude larger than 8192. And then we divide by 2 to
> + * cover a worst-case of every other cpu being on one of two nodes for a
> + * very large NR_CPUS.
> + *
> + *  Use PAGE_SIZE as a minimum for smaller configurations.
> + */
> +#define CPUMAP_FILE_MAX_BYTES  ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \
> +					? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE)
> +#define CPULIST_FILE_MAX_BYTES  (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE)
> +
>  #endif /* __LINUX_CPUMASK_H */
> -- 
> 2.31.1