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Tue, 04 Aug 2026 13:36:22 -0700 (PDT) Message-ID: Subject: Re: [PATCH bpf-next v3 5/9] selftests/bpf: Add kfunc __arena and __arena_nullable argument tests From: Eduard Zingerman To: Kumar Kartikeya Dwivedi , bpf@vger.kernel.org Cc: Tejun Heo , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Emil Tsalapatis , kkd@meta.com, kernel-team@meta.com Date: Tue, 04 Aug 2026 13:36:20 -0700 In-Reply-To: <6022cc53a26ea291178b648a6b07c0e8d6874c70.camel@gmail.com> References: <20260803125115.2264733-1-memxor@gmail.com> <20260803125115.2264733-6-memxor@gmail.com> <7f0d996cbfb2703450b9974d18c9f60ac2a3a959.camel@gmail.com> <4d3b9137362fd9151ecdaf29d863a6cc0b0799d1.camel@gmail.com> <9552fc68c2d06c5dd88bb7494b4934e779bc45c6.camel@gmail.com> <6022cc53a26ea291178b648a6b07c0e8d6874c70.camel@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2-10 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-08-04 at 13:33 -0700, Eduard Zingerman wrote: > On Tue, 2026-08-04 at 22:28 +0200, Kumar Kartikeya Dwivedi wrote: > > On Tue Aug 4, 2026 at 10:26 PM CEST, Eduard Zingerman wrote: > > > On Tue, 2026-08-04 at 13:24 -0700, Eduard Zingerman wrote: > > > > On Tue, 2026-08-04 at 22:14 +0200, Kumar Kartikeya Dwivedi wrote: > > > >=20 > > > > ... > > > >=20 > > > > > > Which leads to several conclusions: > > > > > > - We should reach a consensus regarding KF_ARENA* usage, as the= se > > > > > > =C2=A0 kfuncs would clearly benefit from having __arena annotat= ions on > > > > > > =C2=A0 parameters (on the BPF side, on the host side these shou= ld be > > > > > > =C2=A0 declared as plain pointers). > > > > >=20 > > > > > Yes, but even if we do, for the time begin, we won't have support= for > > > > > automatically emitting it until resolve_btfids changes are done. = That said, I > > > > > can manually add the annotation for now. > > > >=20 > > > > We can fast-track resolve_btfids. > > > >=20 > > > > > > - In patch #1, it appears that there is no need to allow PTR_TO= _ARENA > > > > > > =C2=A0 for parameters passed to such a function. At-least I don= 't see a C > > > > > > =C2=A0 code not involving manual casts that would require such = support. > > > > >=20 > > > > > This one I don't understand. Why wouldn't we get PTR_TO_ARENA typ= ed paramters as > > > > > arguments? > > > >=20 > > > > `(u64 *)val` is translated as an address space cast instruction. > > > > This instruction yields PTR_TO_ARENA. Except for explicit casts, > > > > how else can you pass PTR_TO_ARENA to such a function? > > >=20 > > > For example, `foo->ptr` yields a scalar from the verifier point of vi= ew. > > >=20 > >=20 > > Sure, but I don't think we should reject the case where someone does ex= plicit > > cast. See e.g. the global function __arena tag, which also accepts both= cases. >=20 > PTR_TO_ARENA is already a valid kernel space pointer, it does not need > additional conversion. Nah, that's not true. It is still a 32-bit value.