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 9C027C982EE for ; Mon, 21 Sep 2026 18:39:43 +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:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=3snj98fmjbtANq16+FRyVMqVPheby92j6W8WIjGOO5U=; b=opljAMmye+KUtUMQgKPD+uuo4X SspBchSQRbzz4sQvw4PpakFy5wxLOdbzuYn2BvByNNypuGCubxInd7iQT+cVS12DzSSzKhuTRPX3L ujJxumJzNEIcBhyHIsIMLlkpxncKsKzAkXejee/eNFoSvn/8GcAVnuNw2CH/1p+BZGPycKr81Q2Tn XTs7PtatKCFtib4e/dQMx6rnmOBzXL/RnUfiygxXIXFfamWZArPGO/q1Sv8GH427wPcNPyD/gjFBE gHbN9I0lrdGNoa5TeOBne+c3oYAwfGwAsJzRud2fJYUfOmzOva7okCa5jPAimDYCueekkQFfWJSMu kmL1foRw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x8ivR-00000003995-2c7W; Mon, 21 Sep 2026 18:39:37 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x8ivP-0000000398q-431p for linux-arm-kernel@lists.infradead.org; Mon, 21 Sep 2026 18:39:36 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id D8BEB60008; Mon, 21 Sep 2026 18:39:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65F8A1F000FF; Mon, 21 Sep 2026 18:39:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790015974; bh=3snj98fmjbtANq16+FRyVMqVPheby92j6W8WIjGOO5U=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=jr8/IKplV+dmJmKP3CopP8NRnqIhbL8ZKCRP+bIIpuuEMVbmoILBjslfEmsTzXhgd 80Xid8Aiv7Dm/fZ9FXXOPbtLlcDFsJE9H6zQXmNr32c4X5+It5RqPvu3lJvXS0CovZ C7zQtS0RH9NhGrErWzgjoNrAy9k/Xu2so61zDWM6vjMgb/xDEaGAmFxhIHLeAyssvd 1zlStONeGroUdQXq+7aSu7q9MtE+XSs2N1vlQc5uFQEMlpAg8qP1RONlU5UZOM2mQt 29hrOl0y2kFV0BFWJOteoBIwlIwbWMaf5lppsOL9vA8qv0wqmZ3FcN9SWfy6NK7plP 6zKnVwlD9BnOw== Date: Mon, 21 Sep 2026 11:39:33 -0700 From: Oliver Upton To: "Lorenzo Stoakes (ARM)" Cc: Fuad Tabba , Marc Zyngier , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Will Deacon , Jack Thomson , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] KVM: arm64: Restore the VM's feature bitmap when kvm_setup_vcpu() fails Message-ID: References: <20260921063718.1604533-1-fuad.tabba@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Hey Lorenzo, On Mon, Sep 21, 2026 at 02:34:12PM +0100, Lorenzo Stoakes (ARM) wrote: > On Mon, Sep 21, 2026 at 08:24:56AM +0100, Fuad Tabba wrote: > > Hi Oliver, > > > > On Mon, 21 Sep 2026 00:09:17 -0700, Oliver Upton wrote: > > [...] > > > > Nothing in the tree loads a vCPU whose init failed, so this is latent. > > > > The upcoming series that enables KVM_PRE_FAULT_MEMORY for arm64 exposes > > > > it: the generic kvm_vcpu_pre_fault_memory() calls vcpu_load() whether > > > > or not the vCPU has been initialised. > > > > > > That's a bug, not a feature. We should require an initialized vcpu for > > > the ioctl. > > > > That one is for Lorenzo then :) I'll reword the message so the stale > > bitmap comes first and the pre-fault crash is just how it showed up. > > In general this is the behaviour of _generic_ KVM code > (kvm_vcpu_pre_fault_memory()), which itself does not require an initialised > vCPU, and no other arch seems to requires that either in the arch-specific > pre-fault code. > > The actual pre-faulting implementation intentionally only targets the > canonical MMU to fault in S2 page tables, which doesn't need initialisation > to have taken place AFAICT. > > However I could add: > > if (!kvm_vcpu_initialized(vcpu)) > return -ENOEXEC; > > To kvm_arch_vcpu_pre_fault_memory(), which would make this a requirement, > though that would bring us out of line with other archs. Actually, we need this enforcement to happen before the arch-generic implementation calls vcpu_load(). So that would be some amount of kvm_arch_* boilerplate added to the generic code to enforce this requirement like we do on the other vCPU ioctls. I'm not too worried about aligning this with other architectures; the idea of a half-baked vCPU getting loaded is worrying. > OTOH, I don't see why anybody would pre-fault BEFORE init, feels like > something that should be done later on in VMM bring up right? > > So I doubt doing this would really break any sane user. > > Let me know if you want that change in the series and I can respin it. Please do, thank you for addressing this. Best, Oliver