[RFC/PATCH bpf-next 2/3] mm/bpf: Add bpf_get_slab_cache() kfunc

[Namhyung Kim <namhyung@kernel.org>]

The bpf_get_slab_cache() is to get a slab cache information from a
virtual address like virt_to_cache().  If the address is a pointer
to a slab object, it'd return a valid kmem_cache pointer, otherwise
NULL is returned.

It doesn't grab a reference count of the kmem_cache so the caller is
responsible to manage the access.  The intended use case for now is to
symbolize locks in slab objects from the lock contention tracepoints.

Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 kernel/bpf/helpers.c |  1 +
 mm/slab_common.c     | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 1a43d06eab286c26..03db007a247175c4 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3090,6 +3090,7 @@ BTF_ID_FLAGS(func, bpf_iter_bits_new, KF_ITER_NEW)
 BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)
 BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_get_slab_cache, KF_RET_NULL)
 BTF_KFUNCS_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 7443244656150325..a87adcf182f49fc4 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1322,6 +1322,20 @@ size_t ksize(const void *objp)
 }
 EXPORT_SYMBOL(ksize);
 
+#ifdef CONFIG_BPF_SYSCALL
+__bpf_kfunc_start_defs();
+
+__bpf_kfunc struct kmem_cache *bpf_get_slab_cache(u64 addr)
+{
+	struct slab *slab;
+
+	slab = virt_to_slab((void *)(long)addr);
+	return slab ? slab->slab_cache : NULL;
+}
+
+__bpf_kfunc_end_defs();
+#endif /* CONFIG_BPF_SYSCALL */
+
 /* Tracepoints definitions. */
 EXPORT_TRACEPOINT_SYMBOL(kmalloc);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc);
-- 
2.46.0.792.g87dc391469-goog