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 F24013E49F1; Wed, 5 Aug 2026 08:47:14 +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=1785919636; cv=none; b=UaZgwesnjHMb+vq3SIvS5YZrDV1FSuV+MHSKkhb65L0Zbcgo4kGgBDxz5+2tD11n0r1pOVNiIXDgfazW03nnxi8GS4qyltxz2p7+a+2Fs19BUD+1ktAQpm8BImSskNphMBl8EjW+ZLdEDlpIWx5X690rNgqy5xwRyojG3Nuowms= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785919636; c=relaxed/simple; bh=NCefE1mO1GlvWUkeAoReVC10N2F/jCGs0rCOQGw2TpU=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=qaduHyWtvuBRAOmSEDrK/nuwT+UeF4tcXNdBZZ2V6ABQ1zXQ13CKqFUU5joRJPmhvgWSuhtvG8iKGo/2oq0HPTaxm6gg2J0Ec5bqRab/Ii/xfs43+GorS5GZlCletxa2WtfaZ+xiPHPippGowzLfCplmIylZNzixwQayJmMGqnk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mLJl/Bok; 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="mLJl/Bok" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 714721F000E9; Wed, 5 Aug 2026 08:47:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785919634; bh=kszMkcQKqrIYgW/Oo0EZOBH4I8hWpCPVD1GaXYgTgbg=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=mLJl/BokC8Mo53uR+QWaVydHsO6EXtOh06TDIVqz3tZirYkI2kZ0XrZ+19FdkM3wm d7HWfNeF+4UMGMGz9UZteAlSvRRnWZzeqRyxSyqq6wWn4tJdRfAeek88Yf63oJ6sbR TfUaPxDN4NLSahez5SjUo80Uc5rE/vAyTAR2PvTWdQe3aCEyzBBS7KX1hhDG/nhXsc oY3shvzY0qZDZj2eHBiAzU/Nx7RmGfE0abAFOr6DUatPCZzXUnTJyGF0eLtCpIFQE4 SHx++8Kr/ojSi8BZKfPixbsQ770UCSKncjr9xcZGNqzsIjMXHJF/bZJcBwa7A9yGKc OYW3RQ799aKcg== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wrXHM-0000000CWRv-0CXA; Wed, 05 Aug 2026 08:47:12 +0000 Date: Wed, 05 Aug 2026 09:47:11 +0100 Message-ID: <86cxvxar8w.wl-maz@kernel.org> From: Marc Zyngier To: Jing Zhang ,Mostafa Saleh Cc: KVM , KVMARM , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Paolo Bonzini , Sean Christopherson , Mingwei Zhang , David Matlack Subject: Re: [RFC] KVM: Proposed uAPI for querying GSI and irqbypass status In-Reply-To: References: <20260717162658.2833515-1-jingzhangos@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: jingzhangos@google.com, smostafa@google.com, kvm@vger.kernel.org, kvmarm@lists.linux.dev, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, pbonzini@redhat.com, seanjc@google.com, mizhang@google.com, dmatlack@google.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Wed, 05 Aug 2026 09:26:56 +0100, Mostafa Saleh wrote: > > Hi Jing, > > On Fri, Jul 31, 2026 at 10:26:26AM -0700, Jing Zhang wrote: [drop the LLM generated stuff] > > While interfaces in debugfs are fantastic for manual, retroactive > > debugging on a developer workstation, they are not Dependable for > > fleet-wide observability. This RFC aims to provide a proactive > > monitoring solution that aligns KVM with production operational > > requirements across architectures (both ARM and x86). > > > > Would love to hear your thoughts on this perspective. > > I agree that debugfs is not suitable for that purpose. > > My main concerns are: > 1- Why is /proc/interrupts not enough, it should show whether the > interrupts are going through the host (not bypassed) and it should > show when the host get a doorbell if the vCPU was not resident. This. Also, there is a very long standing ask to represent the output of /proc/interrupts as a structured set, retrieved through a generic kernel interface. I.e. *not* something KVM specific. Everybody asks, nobody does. As usual. And if you are interested in things being "Dependable for fleet-wide observability" (I *love* the LLM-generated jargon), there is no way you can make sense of what the guest sees without looking at the full picture, i.e. the full machine. > 2- Technical feasibility on arm64. Since the host does not have > visibility into interrupts directly injected into the guest, it > cannot accurately maintain the proposed counters vgic_its_vlpis_hw. And GICv5 is going to make things even less observable, as only doorbells fire on the host. My take is that for these, a PMU-type interface is better suited. But in general, a KVM-specific for something that is a system-wide problem is IMO the wrong approach. You may want to put tglx in that loop and see what he has to say. Thanks, M. -- Without deviation from the norm, progress is not possible.