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AJvYcCWA0UgdBRB2oqHqz9kEqb19RzaDk4EQ+54BPDCC/y7Wh5XNN5HYHVOSe2hhl4zRMxyr+c35mGwt5A==@kvack.org X-Gm-Message-State: AOJu0YzJ14NiViux5hOPotFXrWRzfzEBuOjJGPNNQvv0x0LgzxOQkSyo SsZavqN67DGG2B9hm+kXheJX/86wQ8RFgQko6bIdMhH77Ba57TcefiyKgBCBn/UNOeGMHrmjH7H JEOKKG5FRik9xMuvwMIkT6F3mEX8= X-Google-Smtp-Source: AGHT+IGX0N+4Fs+UmGEyD0ArP3gM2Itw+hfw3twUo3F0NHNdaQtjUxWuszfeOZayS3V6VAv+qbBT4OtQz0dHZ+NeE5w= X-Received: by 2002:a05:6000:b4b:b0:37d:5436:49b with SMTP id ffacd0b85a97d-37d86bb9547mr896088f8f.13.1729016722875; Tue, 15 Oct 2024 11:25:22 -0700 (PDT) MIME-Version: 1.0 References: <20241010232505.1339892-1-namhyung@kernel.org> <20241010232505.1339892-3-namhyung@kernel.org> In-Reply-To: From: Alexei Starovoitov Date: Tue, 15 Oct 2024 11:25:11 -0700 Message-ID: Subject: Re: [PATCH v5 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 , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , LKML , bpf , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm , Arnaldo Carvalho de Melo , Kees Cook , "Paul E. McKenney" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: jdhd7rt9nrzztfdojw1aai6it1co3etq X-Rspamd-Queue-Id: D877B20008 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1729016720-41002 X-HE-Meta: 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 P/OpPAB4 oMW24f6BDjQfMCjGEL/iUOIA6Vk5RNRYEJGbdrjNj/HI4tzhD1Xr8uAGS5b+z2SgWRbVbIBHY9F3xaVr8MhuOqCMIqbul7+r3ckUQqzwbMLy1iIJrTchoLEDJpnC6O8LUCXV9mHh/OEGil5WO6OfYmEs+RIO35VWcmd64XfxF5lsqiScqsIGlmvCHsfRRNLHgjRcYYUwiiWG81JF95yIEUo1qbEMQmLyqXy6MaMtaYFHmYkyM/zFd+5pLP0a1GJvAZI7bvHr9r52KHFIWZ1AVvKGczFrRYcjSVtFmBIIJPofSiyQ4zqMNFKDuAS69oA1KcHv9YqdBKSuar3F12MoaVg2pcYXHTs8qE/znSwCUFoYKOklVV2KTS7ETEMer8+zHW4x9aZfLDk02FMANrTZCtTX56h3lGVfsU7ZiBBMnRkn7KlO9op1tDa3LREbkv8JH1zz6bFEjOb/wHWD+ydrEK94M/CkSecV8CrP8bWEtak8iaRo= 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 Tue, Oct 15, 2024 at 11:20=E2=80=AFAM Namhyung Kim = wrote: > > On Mon, Oct 14, 2024 at 06:50:49PM -0700, Alexei Starovoitov wrote: > > On Mon, Oct 14, 2024 at 11:13=E2=80=AFAM Namhyung Kim wrote: > > > > > > Hi Alexei, > > > > > > On Fri, Oct 11, 2024 at 12:14:14PM -0700, Namhyung Kim wrote: > > > > On Fri, Oct 11, 2024 at 11:35:27AM -0700, Alexei Starovoitov wrote: > > > > > On Thu, Oct 10, 2024 at 4:25=E2=80=AFPM Namhyung Kim wrote: > > > > > > > > > > > > The bpf_get_kmem_cache() is to get a slab cache information fro= m a > > > > > > virtual address like virt_to_cache(). If the address is a poin= ter > > > > > > to a slab object, it'd return a valid kmem_cache pointer, other= wise > > > > > > NULL is returned. > > > > > > > > > > > > It doesn't grab a reference count of the kmem_cache so the call= er is > > > > > > responsible to manage the access. The returned point is marked= as > > > > > > PTR_UNTRUSTED. And the kfunc has KF_RCU_PROTECTED as the slab = object > > > > > > might be protected by RCU. > > > > > > > > > > ... > > > > > > +BTF_ID_FLAGS(func, bpf_get_kmem_cache, KF_RCU_PROTECTED) > > > > > > > > > > This flag is unnecessary. PTR_UNTRUSTED can point to absolutely a= ny memory. > > > > > In this case it likely points to a valid kmem_cache, but > > > > > the verifier will guard all accesses with probe_read anyway. > > > > > > > > > > I can remove this flag while applying. > > > > > > > > Ok, I'd be happy if you would remove it. > > > > > > You will need to update the bpf_rcu_read_lock/unlock() in the test co= de > > > (patch 3). I can send v6 with that and Vlastimil's Ack if you want. > > > > Fixed all that while applying. > > > > Could you please follow up with an open-coded iterator version > > of the same slab iterator ? > > So that progs can iterate slabs as a normal for/while loop ? > > I'm not sure I'm following. Do you want a new test program to iterate > kmem_caches by reading list pointers manually? How can I grab the > slab_mutex then? No. See bpf_iter_task_new/_next/_destroy kfuncs and commit c68a78ffe2cb ("bpf: Introduce task open coded iterator kfuncs").