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Fri, 04 Oct 2024 13:11:10 -0700 (PDT) MIME-Version: 1.0 References: <20241002180956.1781008-1-namhyung@kernel.org> <20241002180956.1781008-3-namhyung@kernel.org> In-Reply-To: <20241002180956.1781008-3-namhyung@kernel.org> From: Song Liu Date: Fri, 4 Oct 2024 13:10:58 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v4 bpf-next 2/3] mm/bpf: Add bpf_get_kmem_cache() kfunc To: Namhyung Kim Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , LKML , bpf@vger.kernel.org, Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, Arnaldo Carvalho de Melo , Kees Cook Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C3BF8C000B X-Stat-Signature: rca9r19c7nmdzxkugz63cxwgpcdngthz X-HE-Tag: 1728072673-424029 X-HE-Meta: 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 +9m+Gi6g ja+SBNVhGKT75d6wmS6MXIazqjE1m2SpIzVpvMEk10XriYy5xo3mVHanNmUuFLYVKBto+5jRQwVS2KYl5aJnBiFy3fN7mCKyhmPUwv+lQ9NaIN7ovfxherVquS3m1bMke+trzhTqan6ejW/a8KgApQYAC7KToHPiULkCUrkECGfUH7y1RXk5wdhBWMnUxXX2QxSlW1ZZdbfjWyFOvjaFR8SOafBfFfg0+mLxYqR20+mRLi7AsXcbWuwhqlKtZFu9iz00qH4o63bVnFLgrvGzrh8U4lBErWX69obeO+iwbu+WapN3+PgOdKT7w3A54kC41KG4Hi3uvlR98C/oCzLIz9GH/aQVn3I0rq6SFSpQ7/1QI75ib3RfDYZPTwZ4cYz5M1qhPhJ2Rzv3rUT2yGl3HxhJiBylzVUrdsH1Mknck/p0R71XArszHfzDUBHla3WO0C/30zOputoRnUew= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 2, 2024 at 11:10=E2=80=AFAM Namhyung Kim = wrote: > > The bpf_get_kmem_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 > Acked-by: Roman Gushchin (mm/*) > Acked-by: Vlastimil Babka #mm/slab > Signed-off-by: Namhyung Kim > --- > kernel/bpf/helpers.c | 1 + > mm/slab_common.c | 19 +++++++++++++++++++ > 2 files changed, 20 insertions(+) > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > index 4053f279ed4cc7ab..3709fb14288105c6 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_kmem_cache, KF_RET_NULL) > BTF_KFUNCS_END(common_btf_ids) > > static const struct btf_kfunc_id_set common_kfunc_set =3D { > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 7443244656150325..5484e1cd812f698e 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -1322,6 +1322,25 @@ size_t ksize(const void *objp) > } > EXPORT_SYMBOL(ksize); > > +#ifdef CONFIG_BPF_SYSCALL > +#include > + > +__bpf_kfunc_start_defs(); > + > +__bpf_kfunc struct kmem_cache *bpf_get_kmem_cache(u64 addr) > +{ > + struct slab *slab; > + > + if (!virt_addr_valid(addr)) > + return NULL; > + > + slab =3D virt_to_slab((void *)(long)addr); > + return slab ? slab->slab_cache : NULL; > +} Do we need to hold a refcount to the slab_cache? Given we make this kfunc available everywhere, including sleepable contexts, I think it is necessary. Thanks Song > + > +__bpf_kfunc_end_defs(); > +#endif /* CONFIG_BPF_SYSCALL */ > + > /* Tracepoints definitions. */ > EXPORT_TRACEPOINT_SYMBOL(kmalloc); > EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc); > -- > 2.46.1.824.gd892dcdcdd-goog >