From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 87C82CCFA03 for ; Mon, 3 Nov 2025 08:37:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-ID:Subject:Cc:To: From:Date:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=/6+8IBdXCcTU6eZ4JMuY2we8/fQYN6+oBue210uWprk=; b=LO+BzsefqVHQLGIBK3ip9bTGui nXKNvG+3OUDZWsTiX4IJ8EqY2cLueoSq9al6noV47F9iWKfOzftDQYoc6an153wB/h0ikeq384/Dg jz1Vq4ZRQ7Q6yBgy+ng3wPDCebR5PhCFDgGpPRjuNekj4ypgFX623ckCG0aolZOOzFAZiP7y3SFEq F3i22NCqXMc5n0hwLgDB2LihhhuS1NIXDB9/Zwk8Wl3YKrXpj9YEIZc+jvPhh0QM8HeqSJukSEbS/ spCqgGirIiEmG56BbKPoYGeFyY3CBbHgXjsDx+mIN03aBqk4NGCYuj6f531pb7dPJuQbfXMg833PW rJqgq2ww==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vFq4M-00000009RTb-0tBb; Mon, 03 Nov 2025 08:37:42 +0000 Received: from mail-ed1-x535.google.com ([2a00:1450:4864:20::535]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vFq4J-00000009RSM-2f5t for linux-arm-kernel@lists.infradead.org; Mon, 03 Nov 2025 08:37:41 +0000 Received: by mail-ed1-x535.google.com with SMTP id 4fb4d7f45d1cf-6409cb34fe0so344872a12.3 for ; Mon, 03 Nov 2025 00:37:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1762159057; x=1762763857; darn=lists.infradead.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=/6+8IBdXCcTU6eZ4JMuY2we8/fQYN6+oBue210uWprk=; b=KGLRGCr6hAYuitreTADyMcp5+eFvB+tXFyLH336hSHXQ3jyhAb9BsHBumOE7RAI+mK O/Xm6siv88MQLxDuy/uXSsvoM8WpIXwHfy6ZjeS45ZXkk7on+rjjgugKukVsIyZ7j964 o4VLAc7MtCqPHQWKGho1h4oReP8qK8BrRFPNSnKQ+fTZUhhu03RJX3L8LEs5Qsv51R+o ov5p3sJpqyz1rDX4m5IgUB3aNoXILeXjU1Fd6jVt/0ZTy7EfzkiTbBks7hhH/yqEFnlB gsJEVsIs0EtmI4zLM8gUVUSDiN/5OK/2vDPA8kzyXuAj0MMKALaMTNPIbuA7z7lIS+l0 IqSw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1762159057; x=1762763857; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=/6+8IBdXCcTU6eZ4JMuY2we8/fQYN6+oBue210uWprk=; b=jNm+GvZDCCjji2qD7/o4XXt++3OsS1m6+u1f6JOZQG90kpfj7lT+l/kMoekxzkVg7b yG8VrohjsW5NH1uB3/ryhX4BF/Rne7p+c04CcKfY/YD9E2KUgo0FNc8fOPXVo0Ofn6C9 DkNhw2bMxAuV0oMBtEzXcZh8s6XfmdCtqYTZAuWbwKK4As46Bc9CzdM5j1Mi/wwhZLn3 Ya3ldD83BBMTConBdR48kyCETTVT6CyIgpfw8bjB2qlQ6+4MBBB8UTrlIapDgL4ew8V7 bZ8JLCZGlU/zS350gfjdQljKh283y5kFhF0gURPK3saYKEefj4G0MUhfo9wuWmy/cHub vbmA== X-Forwarded-Encrypted: i=1; AJvYcCVmXTdXlTVnuyruNswpHEaQluZOnnR+Q46ODXd9xtlH/61hbsgF0PgIDYtqBgPiQrDhPahbuy1IIaOhgFmJysv3@lists.infradead.org X-Gm-Message-State: AOJu0YwA4G80o0gx0IgUMgEcWjR1hObdWVjMi0X5W7RgMo0g0ZgXIIzG Eq4CjmIJN3TKYLmGcRcU7TRhwBXbCrj/k0zEMYh+JtFOhURtFvbMdHY/qpi9+PWNI+s= X-Gm-Gg: ASbGncvq7zTToIkIGfXd8gEDhXaFqakPlvpTqU2avskYE9sjqvHCTqff64G0Im1e4+C tiUEsz9WYdp8U86tBpQBLWSvr9e5dR2OQo8umveHvOsfututeux9UXH10/hkb64yPOzAn78D6eI rXONL9JcRIDkhiYqwUIn52DD5FymuM7zYEiG6OtnPGyS+aQ4ObFeBTkrhdTLDc73ij3v6iYi6HF HQgUjF2IdAbqUvgS54mHP7ajn+QRodHm1tHGmtT28N15s3MK/k+tItJwxo5JUsq4IZx2E7jt4so qlVwzUHZJaenaFRon2Vr9VMopBS5jsd2CzX3QVQvwiCnrtsOZxaUWBNXc/ik4yxI8HUN8e+iT0m ix2GNBdAGmTUvMV0u78q6/P8cP3tU0Dw3x+UEZw8Mc9UD/iO3m1ORbkvEvbXT6wFPae44ynqWJV +RpV+AUX9dBaQEMUiQb3TAbgr1WrW7+fJ1fFpA+cztefS1pH2fmWHX9xWuCidth9T0JJ7j29/tu 9I8 X-Google-Smtp-Source: AGHT+IEXAMzB4Q3iZseWqc5EI+3z01yD/lkzyZQiHdGqXZRiWGSYaalZ7FPGcsDnEnqBbvKYbK1akQ== X-Received: by 2002:a05:6402:27d3:b0:640:9eb3:3683 with SMTP id 4fb4d7f45d1cf-6409eb34460mr3244974a12.1.1762159057100; Mon, 03 Nov 2025 00:37:37 -0800 (PST) Received: from mordecai (dynamic-2a00-1028-83b8-1e7a-3010-3bd6-8521-caf1.ipv6.o2.cz. [2a00:1028:83b8:1e7a:3010:3bd6:8521:caf1]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6407b428119sm9012005a12.24.2025.11.03.00.37.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Nov 2025 00:37:36 -0800 (PST) Date: Mon, 3 Nov 2025 09:37:28 +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: <20251103093728.031042d0@mordecai> In-Reply-To: References: <20251010153839.151763-1-vschneid@redhat.com> <20251010153839.151763-7-vschneid@redhat.com> <20251030112251.5afcf9ed@mordecai> X-Mailer: Claws Mail 4.3.1 (GTK 3.24.50; x86_64-suse-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251103_003739_707157_5F319044 X-CRM114-Status: GOOD ( 39.10 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 31 Oct 2025 12:52:56 +0100 Valentin Schneider wrote: > On 30/10/25 11:25, Petr Tesarik wrote: > > 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. > > > > I was about to write such a comment but I had another take; The _NOINSTR > static key helpers are special and only relevant to IPI deferral; whereas > the _RO helpers actually change the backing storage for the keys and as a > bonus are used by the IPI deferral instrumentation. > > IMO it's the same here for the static calls, it makes sense to mark the > relevant ones as _RO regardless of IPI deferral. > > I could however add a comment to ANNOTATE_NOINSTR_ALLOWED() itself, > something like: > > ``` > /* > * This is used to tell objtool that a given static key is safe to be used > * within .noinstr code, and it doesn't need to generate a warning about it. > * > * For more information, see tools/objtool/Documentation/objtool.txt, > * "non-RO static key usage in noinstr code" > */ > #define ANNOTATE_NOINSTR_ALLOWED(key) __ANNOTATE_NOINSTR_ALLOWED(key) > ``` I agree, this makes more sense. Thank you! Petr T