[PATCH 2/5] slab_id: Generic slab ID infrastructure

[Pavel Emelyanov <xemul@parallels.com>]

The idea of how to generate and ID for an arbitrary slab object is simple:

- The ID is 128 bits
- The upper 64 bits are slab ID
- The lower 64 bits are object index withing a slab (yes, it's too many,
  but is done for simplicity - not to deal with 96-bit numbers)
- The slab ID is the 48-bit per-cpu monotonic counter mixed with 16-bit
  cpuid. Even if being incremented 1M times per second the first part
  will stay uniqe for 200+ years. The cpuid is required to make values
  picked on two cpus differ.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

---
 include/linux/slab.h |   17 +++++++++++++++++
 init/Kconfig         |    9 +++++++++
 mm/Makefile          |    1 +
 mm/slab_obj_ids.c    |   25 +++++++++++++++++++++++++
 4 files changed, 52 insertions(+), 0 deletions(-)
 create mode 100644 mm/slab_obj_ids.c

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 573c809..ae9c735 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -23,6 +23,7 @@
 #define SLAB_CACHE_DMA		0x00004000UL	/* Use GFP_DMA memory */
 #define SLAB_STORE_USER		0x00010000UL	/* DEBUG: Store the last owner for bug hunting */
 #define SLAB_PANIC		0x00040000UL	/* Panic if kmem_cache_create() fails */
+#define SLAB_WANT_OBJIDS	0x00080000UL	/* Want GENERIC_OBJECT_IDS-friendly slabs */
 /*
  * SLAB_DESTROY_BY_RCU - **WARNING** READ THIS!
  *
@@ -162,6 +163,22 @@ void kfree(const void *);
 void kzfree(const void *);
 size_t ksize(const void *);
 
+#ifdef CONFIG_SLAB_OBJECT_IDS
+void __slab_pick_id(u64 *s_id);
+static inline void __slab_get_id(u64 *id, u64 s_id, u64 o_id)
+{
+	id[0] = o_id;
+	id[1] = s_id;
+}
+
+void k_object_id(const void *, u64 *id);
+#else
+static inline void k_object_id(const void *x, u64 *id)
+{
+	id[0] = id[1] = 0;
+}
+#endif
+
 /*
  * Allocator specific definitions. These are mainly used to establish optimized
  * ways to convert kmalloc() calls to kmem_cache_alloc() invocations by
diff --git a/init/Kconfig b/init/Kconfig
index d627783..4c1c0e6 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1200,6 +1200,15 @@ config SLUB_DEBUG
 	  SLUB sysfs support. /sys/slab will not exist and there will be
 	  no support for cache validation etc.
 
+config SLAB_OBJECT_IDS
+	default y
+	bool "Enable slab kernel object ID infrastructure"
+	depends on !SLOB
+	help
+	  This option provides an infrastructure for calculating ID-s of
+	  slab/slub objects. These ID-s are not based on the object location
+	  in memory and thus can be shown to the userspace.
+
 config COMPAT_BRK
 	bool "Disable heap randomization"
 	default y
diff --git a/mm/Makefile b/mm/Makefile
index 836e416..fb65080 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -50,3 +50,4 @@ obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
 obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
 obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
 obj-$(CONFIG_CLEANCACHE) += cleancache.o
+obj-$(CONFIG_SLAB_OBJECT_IDS) += slab_obj_ids.o
diff --git a/mm/slab_obj_ids.c b/mm/slab_obj_ids.c
new file mode 100644
index 0000000..87d1693
--- /dev/null
+++ b/mm/slab_obj_ids.c
@@ -0,0 +1,25 @@
+#include <linux/percpu.h>
+
+#define SLUB_ID_CPU_SHIFT	16
+static DEFINE_PER_CPU(u64, slub_ids);
+
+void __slab_pick_id(u64 *s_id)
+{
+	int cpu;
+	u64 id;
+
+	/*
+	 * The idea behind this all is very simple:
+	 *
+	 * The ID is the 48-bit per-cpu monotonic counter mixed with 16-bit cpuid.
+	 * Even if being incremented 1M times per second the first part will stay
+	 * uniqe for 200+ years. The cpuid is required to make values picked on
+	 * two cpus differ.
+	 */
+
+	cpu = get_cpu();
+	id = ++per_cpu(slub_ids, cpu);
+	WARN_ON_ONCE(id >> (64 - SLUB_ID_CPU_SHIFT) != 0);
+	*s_id = (id << SLUB_ID_CPU_SHIFT) | cpu;
+	put_cpu();
+}
-- 
1.5.5.6

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