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 4A4B12868AB for ; Sun, 26 Jul 2026 13:55:56 +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=1785074157; cv=none; b=rttwGYhhZWPHvFnSfX192UrYvQKNiBH7Kkq5fZ6zE2Meu1xJOS6W18H5MBO5UqaPfpRloEllTqsTbAAy4LTYY6Qy1nGOgYdZBMyfFNj8RpQ4GhYcr19/DQxWGNcFwCT3HQ8qtyAk0cJ7jajZG5M98z3G0GirufgCTuOb6VQXHU8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785074157; c=relaxed/simple; bh=SOCNAPSnPEnPy2s0YfRv1gTaXdKcTDWc5nVM5gXLXMk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=S6Z6q5OhKmhpiOIJ2F1fJAe4IbE7xgkdvjiD+zEKMMbElqBqZxZnbo9XQFMLUz/wfOUBge37kuz1luh1KHBg0BGkK+15pzABqcDvbm1qD9DKfyapwYGxQihj9Bk5VifNN6F64pyqTdEAWyjWQIlXKW8EDzVhrgfVnXXM5N4zARI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GaFtuCkn; 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="GaFtuCkn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5BA6F1F000E9; Sun, 26 Jul 2026 13:55:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785074155; bh=oAqk85PfaZIsBzhpoLVWf76ojRfZbMog0/3PXdHaiAw=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=GaFtuCkngOK2YnYTN5/q1DxREdA9n0YxnFFD94dlpKPeV3syaV9BEWdXFYPnF4n5N zGLMhdZFa28zts7sn8Bzmk0pHrqOb/+bDN7q7f3wObebhZqopz9XqGS+9/MEKSeYNl niKRlm85gzOm0xGyRX9mG0FPZNK7UCeJwnVbFHkjokRX0yoJUn+8XGhNsCpW4eot6I tnWFVx6uLM9kwbSLf0AtmgMP58VWEbC1iTdyyj0s2PQyOggZYk4JS0lXXVdmP/dP4G tG2DtyTYxzy+vTTkuT+JuPligFgrrZC4fa4jHGI18KE1STuiFl/8zs32AvWKvilG3k wBDslo24px5YA== Date: Sun, 26 Jul 2026 14:55:49 +0100 From: Will Deacon To: Kiryl Shutsemau 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 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. 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? Cheers, Will