cpu: add generic support for CPU feature based module autoloading

This patch adds support for advertising optional CPU features over udev
using the modalias, and for declaring compatibility with/dependency upon
such a feature in a module.

The mapping between feature numbers and actual features should be provided
by the architecture in a file called <asm/cpufeature.h> which exports the
following functions/macros:
- cpu_feature(FEAT), a preprocessor macro that maps token FEAT to a
  numeric index;
- bool cpu_have_feature(n), returning whether this CPU has support for
  feature #n;
- MAX_CPU_FEATURES, an upper bound for 'n' in the previous function.

The feature can then be enabled by setting CONFIG_GENERIC_CPU_AUTOPROBE
for the architecture.

For instance, a module that registers its module init function using

  module_cpu_feature_match(FEAT_X, module_init_function)

will be probed automatically when the CPU's support for the 'FEAT_X'
feature is advertised over udev, and will only allow the module to be
loaded by hand if the 'FEAT_X' feature is supported.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 53 insertions, 5 deletions

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index ec36e7772e57..3f0d3732df7f 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -185,6 +185,14 @@ config GENERIC_CPU_DEVICES
         bool
         default n
 
+config HAVE_CPU_AUTOPROBE
+        def_bool ARCH_HAS_CPU_AUTOPROBE
+
+config GENERIC_CPU_AUTOPROBE
+        bool
+        depends on !ARCH_HAS_CPU_AUTOPROBE
+        select HAVE_CPU_AUTOPROBE
+
 config SOC_BUS
         bool
 
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index f48370dfc908..8a38bf8c792f 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -15,6 +15,7 @@
 #include <linux/percpu.h>
 #include <linux/acpi.h>
 #include <linux/of.h>
+#include <linux/cpufeature.h>
 
 #include "base.h"
 
@@ -286,6 +287,45 @@ static void cpu_device_release(struct device *dev)
          */
 }
 
+#ifdef CONFIG_HAVE_CPU_AUTOPROBE
+#ifdef CONFIG_GENERIC_CPU_AUTOPROBE
+static ssize_t print_cpu_modalias(struct device *dev,
+                                  struct device_attribute *attr,
+                                  char *buf)
+{
+        ssize_t n;
+        u32 i;
+
+        n = sprintf(buf, "cpu:type:" CPU_FEATURE_TYPEFMT ":feature:",
+                    CPU_FEATURE_TYPEVAL);
+
+        for (i = 0; i < MAX_CPU_FEATURES; i++)
+                if (cpu_have_feature(i)) {
+                        if (PAGE_SIZE < n + sizeof(",XXXX\n")) {
+                                WARN(1, "CPU features overflow page\n");
+                                break;
+                        }
+                        n += sprintf(&buf[n], ",%04X", i);
+                }
+        buf[n++] = '\n';
+        return n;
+}
+#else
+#define print_cpu_modalias      arch_print_cpu_modalias
+#endif
+
+static int cpu_uevent(struct device *dev, struct kobj_uevent_env *env)
+{
+        char *buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
+        if (buf) {
+                print_cpu_modalias(NULL, NULL, buf);
+                add_uevent_var(env, "MODALIAS=%s", buf);
+                kfree(buf);
+        }
+        return 0;
+}
+#endif
+
 /*
  * register_cpu - Setup a sysfs device for a CPU.
  * @cpu - cpu->hotpluggable field set to 1 will generate a control file in
@@ -306,8 +346,8 @@ int register_cpu(struct cpu *cpu, int num)
         cpu->dev.offline_disabled = !cpu->hotpluggable;
         cpu->dev.offline = !cpu_online(num);
         cpu->dev.of_node = of_get_cpu_node(num, NULL);
-#ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
-        cpu->dev.bus->uevent = arch_cpu_uevent;
+#ifdef CONFIG_HAVE_CPU_AUTOPROBE
+        cpu->dev.bus->uevent = cpu_uevent;
 #endif
         cpu->dev.groups = common_cpu_attr_groups;
         if (cpu->hotpluggable)
@@ -330,8 +370,8 @@ struct device *get_cpu_device(unsigned cpu)
 }
 EXPORT_SYMBOL_GPL(get_cpu_device);
 
-#ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
-static DEVICE_ATTR(modalias, 0444, arch_print_cpu_modalias, NULL);
+#ifdef CONFIG_HAVE_CPU_AUTOPROBE
+static DEVICE_ATTR(modalias, 0444, print_cpu_modalias, NULL);
 #endif
 
 static struct attribute *cpu_root_attrs[] = {
@@ -344,7 +384,7 @@ static struct attribute *cpu_root_attrs[] = {
         &cpu_attrs[2].attr.attr,
         &dev_attr_kernel_max.attr,
         &dev_attr_offline.attr,
-#ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
+#ifdef CONFIG_HAVE_CPU_AUTOPROBE
         &dev_attr_modalias.attr,
 #endif
         NULL