From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 96516246783 for ; Sun, 26 Jul 2026 18:35:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785090925; cv=none; b=OYSQ2hjSTuKH7LWmTVsVT6cSM9AoOOJbWBmW2ggNNk5skrP12jMrA7DIg3sgqZft09RMngOPpytfbf67kA8JMobfkNemiaybmEMKUkdnPDl8MMeyN7JyVPT/H8c0/HSbHzxB+mfUiPG8/bojq7LEDW/vmSyF9If5DR5GSoMzpeQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785090925; c=relaxed/simple; bh=NasJm6Uk8dDP/Ysy7eKaDahvUNSgH0uS2Mj5n3d+bAM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MgGwVqjuS0VYWfj043AHBTR43rrmZ5pQk/4Eg++mRM9bfWJqzlp1LjfSJNiwnuG/+8YgAKvCistCA8/e0TdXN0W8NWj0ScuihyRFBjf1r2AHUAt+QLFLAwBHIx8Wh3QboodzPRdZbR6uvIcgp7WAMft+pteg+LXDMjHPVFTA6e4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fce73Hj5; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fce73Hj5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 675F21F00A3A; Sun, 26 Jul 2026 18:35:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785090924; bh=bajTzRfqbEOMEZh0AynaaPxjycs9nvGrQz4Q0pmWNeM=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=fce73Hj5N+/AzPrSShZX+VlGeVnIjeqGBQFx/3d4zgTqVdX+KL6PdAV9JBO/LKN7V HReUjnZVtZ9JQXutwLewQ1zx3iUlv8TwPz/u3p6Az9Rp+NuJnudiAcd+kRjnhv/X2J t5xxpGmgEqqQHKYsFCCSwMoAztyeUlDskUyad5obMVRhbLht1tSJ7Wc3jUS6UEpNLF SFCnMSgufbby15MVAhEqeRKEAjDB7Ipv7BuUEotN7+Yp5ET15PKPpNPpqi93ToD4qo jGM+bOzTvWFYpe8/DZw3bUN7HEgpj/0qkfiUBpQJ3odDQbT5yW1A5YT49kCLQRc6c6 LBd5i2UTCn3GA== Received: from phl-compute-05.internal (phl-compute-05.internal [10.202.2.45]) by mailfauth.phl.internal (Postfix) with ESMTP id 8399EF40084; Sun, 26 Jul 2026 14:35:22 -0400 (EDT) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-05.internal (MEProxy); Sun, 26 Jul 2026 14:35:22 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: dmFkZTG0EtMps4K7/E77adivV7MLv/F4vqy+iYJ5InaxdmJRYEik2jKa1rYpVtZnOdebxQ SXIlXAaWVJgfp/tPj5wNe+YwQOIRA3SDq5+iadpdhUxiJeZkK1C10QzRW8JfZTm/EBDpn6 UzNjVNWszpBmZh5SYPfxQ5md0w+Fi3DlaEz/huniQkb2iwl68tpEyJA5P13SXw7JaiLRWi PeT8lZqONfwPBGo5WIadhRrwtW7gI89J2/nzKwuuRcEPfcF3MvqoI/MUwr/ZAgNK7mjvbh 0NlA4cJsxkg61OZocgbbAbaiKgCsHS5spNdylzzhuk2DGr1uYmtMN2D1XDI7GrXHpxUMlS vz8sF1e8okDfSs/+xdJ1dPmNPyhO/PQW+FNkBr6cu/TuYQcEQfi3ORC39LTnUC4KmZnFb1 wkew+Aj1Ycs2wtSnCBA77qOOD2btaMWnjyJoRKaqyUTLWAL5NKVkSl/sKVP/dlm27qznsU gK0b4ykKUzA5uG+nm/uYG3LgJOq6wdlTEMUqBnJpagMKsH/sUlS/Ltsr/XkLuG7E+CNwgt YbKZnRDr+EQ+1xoKOup25xkv8ndAnZaAwCL2YxVOu0ZxTFvmA4gOKaBg4vLQHJcSMM0pLr ZKNPf425Z2RgkFFA9n36/4cnclroQALPVUm6qkzQ8jMpqOgFWrI/EtvoqOUg X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Sun, 26 Jul 2026 14:35:21 -0400 (EDT) Date: Sun, 26 Jul 2026 19:35:20 +0100 From: Kiryl Shutsemau To: Will Deacon Cc: Catalin Marinas , James Morse , Mark Rutland , Marc Zyngier , Doug Anderson , Petr Mladek , Thomas Gleixner , Andrew Morton , Baoquan He , Puranjay Mohan , Usama Arif , Breno Leitao , Julien Thierry , Lecopzer Chen , Sumit Garg , kernel-team@meta.com, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 0/4] arm64: cross-CPU NMI via SDEI Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sun, Jul 26, 2026 at 02:55:49PM +0100, Will Deacon wrote: > On Thu, Jul 09, 2026 at 05:16:37PM +0100, Kiryl Shutsemau wrote: > > On Mon, Jun 29, 2026 at 04:07:14PM +0100, Kiryl Shutsemau wrote: > > > From: "Kiryl Shutsemau (Meta)" > > > > > > A class of debug/observability features needs to interrupt a CPU that has > > > its interrupts locally masked: the all-CPU backtrace behind sysrq-l / > > > RCU-stall / hung-task / hard-lockup dumps, and crash_smp_send_stop() > > > capturing a stuck CPU's state into the vmcore. On arm64 these need a > > > mechanism that reaches a CPU spinning with DAIF masked, which a normal IPI > > > cannot. > > > > Gentle ping. Any feedback? > > > > I'm looking forward to finding an upstreamable solution to the problem. > > This is all pretty small, self-contained and it's useful to you, so I'm > inclined to merge it. Thanks! > However, the one vague concern I have is about the direction of SDEI in > the future. AFAIK, the TF-A implementation is known to have issues, it's > not supported at all by R-FA and I worry that the spec is going to fall > behind the architecture, particularly as FEAT_NMI becomes available. > > So it would be good to understand what we're signing up to maintain here. > Kiryl, do you see an (eventual) migration over to FEAT_NMI, giving us a > path to deprecating SDEI altogether, or do you think the two will live > alongside each other for the forseeable future? Realistically, the foreseeable future. FEAT_NMI is the endgame and a machine that has it needs none of this, but non-FEAT_NMI parts stay in fleets for many years, so I can't honestly give you a date for dropping SDEI. While this change is pretty self-contained, I understand that SDEI infra maintenance can be a burden. Is there anything on the wider SDEI infrastructure that would lower the maintenance burden or keep it more out of your way -- consolidation, tighter isolation, docs, help carrying it? If there's work there that makes SDEI more palatable to keep while non-FEAT_NMI parts are in service, I'm glad to take it on. -- Kiryl Shutsemau / Kirill A. Shutemov