[RFC PATCH v1 30/57] drivers/base: Remove PAGE_SIZE compile-time constant assumption

Ryan Roberts
2024-10-14T12:06:15Z

To prepare for supporting boot-time page size selection, refactor code
to remove assumptions about PAGE_SIZE being compile-time constant. Code
intended to be equivalent when compile-time page size is active.

Update BUILD_BUG_ON() to test against page size limits.

CPUMAP_FILE_MAX_BYTES and CPULIST_FILE_MAX_BYTES are both defined
relative to PAGE_SIZE, so when these values are assigned to global
variables via BIN_ATTR_RO(), let's wrap them with
DEFINE_GLOBAL_PAGE_SIZE_VAR() so that their assignment can be deferred
until boot-time.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---

***NOTE***
Any confused maintainers may want to read the cover note here for context:
https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/

drivers/base/node.c | 6 +++---
drivers/base/topology.c | 32 ++++++++++++++++----------------
include/linux/cpumask.h | 5 +++++
3 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index eb72580288e62..30e6549e4c438 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, CPUMAP_FILE_MAX_BYTES);
+static CPU_FILE_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, CPULIST_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(cpulist, CPULIST_FILE_MAX_BYTES);

/**
* struct node_access_nodes - Access class device to hold user visible
@@ -558,7 +558,7 @@ static ssize_t node_read_distance(struct device *dev,
* buf is currently PAGE_SIZE in length and each node needs 4 chars
* at the most (distance + space or newline).
*/
- BUILD_BUG_ON(MAX_NUMNODES * 4 > PAGE_SIZE);
+ BUILD_BUG_ON(MAX_NUMNODES * 4 > PAGE_SIZE_MIN);

for_each_online_node(i) {
len += sysfs_emit_at(buf, len, "%s%d",
diff --git a/drivers/base/topology.c b/drivers/base/topology.c
index 89f98be5c5b99..bdbdbefd95b15 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, CPUMAP_FILE_MAX_BYTES);
-static BIN_ATTR_RO(thread_siblings_list, CPULIST_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(thread_siblings, CPUMAP_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(thread_siblings_list, CPULIST_FILE_MAX_BYTES);

define_siblings_read_func(core_cpus, sibling_cpumask);
-static BIN_ATTR_RO(core_cpus, CPUMAP_FILE_MAX_BYTES);
-static BIN_ATTR_RO(core_cpus_list, CPULIST_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(core_cpus, CPUMAP_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(core_cpus_list, CPULIST_FILE_MAX_BYTES);

define_siblings_read_func(core_siblings, core_cpumask);
-static BIN_ATTR_RO(core_siblings, CPUMAP_FILE_MAX_BYTES);
-static BIN_ATTR_RO(core_siblings_list, CPULIST_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(core_siblings, CPUMAP_FILE_MAX_BYTES);
+static CPU_FILE_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, CPUMAP_FILE_MAX_BYTES);
-static BIN_ATTR_RO(cluster_cpus_list, CPULIST_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(cluster_cpus, CPUMAP_FILE_MAX_BYTES);
+static CPU_FILE_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, CPUMAP_FILE_MAX_BYTES);
-static BIN_ATTR_RO(die_cpus_list, CPULIST_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(die_cpus, CPUMAP_FILE_MAX_BYTES);
+static CPU_FILE_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, CPUMAP_FILE_MAX_BYTES);
-static BIN_ATTR_RO(package_cpus_list, CPULIST_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(package_cpus, CPUMAP_FILE_MAX_BYTES);
+static CPU_FILE_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, CPUMAP_FILE_MAX_BYTES);
-static BIN_ATTR_RO(book_siblings_list, CPULIST_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(book_siblings, CPUMAP_FILE_MAX_BYTES);
+static CPU_FILE_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, CPUMAP_FILE_MAX_BYTES);
-static BIN_ATTR_RO(drawer_siblings_list, CPULIST_FILE_MAX_BYTES);
+static CPU_FILE_BIN_ATTR_RO(drawer_siblings, CPUMAP_FILE_MAX_BYTES);
+static CPU_FILE_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 53158de44b837..f654b4198abc2 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -1292,4 +1292,9 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask,
? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE)
#define CPULIST_FILE_MAX_BYTES (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE)

+#define CPU_FILE_BIN_ATTR_RO(_name, _size) \
+ DEFINE_GLOBAL_PAGE_SIZE_VAR(struct bin_attribute, \
+ bin_attr_##_name, \
+ __BIN_ATTR_RO(_name, _size))
+
#endif /* __LINUX_CPUMASK_H */
--
2.43.0