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AJvYcCWK1RQl4fABbte07hhmlQBaeEVeBRJMlQEm/T78vLQojK5A1C/mt4u98mbF4xx7y5IweA0cl/FNyw==@kvack.org X-Gm-Message-State: AOJu0YxtJDyGr1fVDGMWdbIjFfPqolzN3vzeA2YrJ9I3CoksZuKkb9Ao MbGqgg6mQ42mII7s7is0sOyU1dS+hvht2Me1Ug0rmbIzzdPPke0FQ1gn4K+iOL6kMuqxBfr7cix sMLW310ZNWxLAr4/AYwlYQWbpMyg= X-Google-Smtp-Source: AGHT+IGZi2ojXKY51cROyUPSMxt2G0s4map61sfmzgoTA1mMLzPAGGlrJLO9s55yFhWLECl3B6S2D6QvFfDch43G/IU= X-Received: by 2002:a5d:498e:0:b0:37d:4eeb:7370 with SMTP id ffacd0b85a97d-37d601fb914mr412209f8f.56.1728671738773; Fri, 11 Oct 2024 11:35:38 -0700 (PDT) MIME-Version: 1.0 References: <20241010232505.1339892-1-namhyung@kernel.org> <20241010232505.1339892-3-namhyung@kernel.org> In-Reply-To: <20241010232505.1339892-3-namhyung@kernel.org> From: Alexei Starovoitov Date: Fri, 11 Oct 2024 11:35:27 -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-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 256FF100013 X-Stat-Signature: pgp7c8ue5fp514b57rfay37dntd44s1s X-HE-Tag: 1728671734-359556 X-HE-Meta: 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 /CQ6y+Iv 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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 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 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 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 any 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.