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[2a00:1028:83b8:1e7a:3010:3bd6:8521:caf1]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b6d853c549fsm1728375066b.37.2025.10.30.03.25.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Oct 2025 03:25:14 -0700 (PDT) Date: Thu, 30 Oct 2025 11:25:03 +0100 From: Petr Tesarik To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, rcu@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Josh Poimboeuf , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Arnaldo Carvalho de Melo , Paolo Bonzini , Arnd Bergmann , Frederic Weisbecker , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Sami Tolvanen , "David S. Miller" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Mel Gorman , Andrew Morton , Masahiro Yamada , Han Shen , Rik van Riel , Jann Horn , Dan Carpenter , Oleg Nesterov , Juri Lelli , Clark Williams , Yair Podemsky , Marcelo Tosatti , Daniel Wagner Subject: Re: [PATCH v6 06/29] static_call: Add read-only-after-init static calls Message-ID: <20251030112251.5afcf9ed@mordecai> In-Reply-To: <20251010153839.151763-7-vschneid@redhat.com> References: <20251010153839.151763-1-vschneid@redhat.com> <20251010153839.151763-7-vschneid@redhat.com> X-Mailer: Claws Mail 4.3.1 (GTK 3.24.50; x86_64-suse-linux-gnu) Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 10 Oct 2025 17:38:16 +0200 Valentin Schneider wrote: > From: Josh Poimboeuf > > Deferring a code patching IPI is unsafe if the patched code is in a > noinstr region. In that case the text poke code must trigger an > immediate IPI to all CPUs, which can rudely interrupt an isolated NO_HZ > CPU running in userspace. > > If a noinstr static call only needs to be patched during boot, its key > can be made ro-after-init to ensure it will never be patched at runtime. > > Signed-off-by: Josh Poimboeuf > --- > include/linux/static_call.h | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/include/linux/static_call.h b/include/linux/static_call.h > index 78a77a4ae0ea8..ea6ca57e2a829 100644 > --- a/include/linux/static_call.h > +++ b/include/linux/static_call.h > @@ -192,6 +192,14 @@ extern long __static_call_return0(void); > }; \ > ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func) > > +#define DEFINE_STATIC_CALL_RO(name, _func) \ > + DECLARE_STATIC_CALL(name, _func); \ > + struct static_call_key __ro_after_init STATIC_CALL_KEY(name) = {\ > + .func = _func, \ > + .type = 1, \ > + }; \ > + ARCH_DEFINE_STATIC_CALL_TRAMP(name, _func) > + > #define DEFINE_STATIC_CALL_NULL(name, _func) \ > DECLARE_STATIC_CALL(name, _func); \ > struct static_call_key STATIC_CALL_KEY(name) = { \ > @@ -200,6 +208,14 @@ extern long __static_call_return0(void); > }; \ > ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) > > +#define DEFINE_STATIC_CALL_NULL_RO(name, _func) \ > + DECLARE_STATIC_CALL(name, _func); \ > + struct static_call_key __ro_after_init STATIC_CALL_KEY(name) = {\ > + .func = NULL, \ > + .type = 1, \ > + }; \ > + ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name) > + I think it would be a good idea to add a comment describing when these macros are supposed to be used, similar to the explanation you wrote for the _NOINSTR variants. Just to provide a clue for people adding a new static key in the future, because the commit message may become a bit hard to find if there are a few cleanup patches on top. Just my two cents, Petr T