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 51842C982EE for ; Mon, 21 Sep 2026 13:34:27 +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=uPds00CPuo0sl2ypaQ/wdQWyadF9e46X9vKuCNW/M40=; b=iWJrFkdQc/9FGCTCsUKSZoPPgz GE0GkcILhUNBWw3cIO7mJvyWpmvjc1m5k1F+ljem4Fnka6LJeELWyfwTsVWtdAo+lQ/iocHmNJ1ju lqh0y5eHIcwfI3cCUeBc6q5xOrGiSlFoqftLLG8UPX/i91estvgMiP8v0be3THnXfWaJ/aR1VTGli uNZ031JkGKjtwR+j2ZuH9lmJHVutLLEtb7uiElnfQAjFF1okkcX4DvrG2jVXr+l7nL2BxZN4eHW2j iFOpuNIfsqTypoNR41or/VxgzfHjiSx93RSZ0wXCH+Q2uYE87lA69qKAjkPkvq+ZGX+YaIynKd/3d y6pI/JJQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x8eA1-00000002FnW-0Fpv; Mon, 21 Sep 2026 13:34:21 +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 1x8e9z-00000002Fmz-2qZe for linux-arm-kernel@lists.infradead.org; Mon, 21 Sep 2026 13:34:19 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id D0637600C8; Mon, 21 Sep 2026 13:34:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 52FBC1F000FF; Mon, 21 Sep 2026 13:34:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789997658; bh=uPds00CPuo0sl2ypaQ/wdQWyadF9e46X9vKuCNW/M40=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=SSXwlK38kiauqEhRh8+Pr0Ahx3wVZ6QcaM1Mm03CqCH91GgKLTwH/LxcxFLbVO4Zi Fb8yRSey5wxIspybcq4fckdmq9+PkSFg47BLm9udssp5v+0jTutqSdQ1Akk4Wfohhe loJGZ8Qi53PPffCB8DpvFsyTYwJzHKXWhRERxkSC+mxrUP/6UO1z3uiRBI005jZEm3 P5rNM/uZNUWZ7zbgwG2kg7GtfmM3sckK3Ow+5DrF+KDUDHOlW+K0dSUM4uQfASGmz8 59D6eS5pQyGD09iMfU48lSzvSyaQ8HBd2clEYyVbp+U8zlpMzqusbkFieywHlPkOf5 wTaBuLxz097tQ== Date: Mon, 21 Sep 2026 14:34:12 +0100 From: "Lorenzo Stoakes (ARM)" To: Oliver Upton 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 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. 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. -- Cheers, Lorenzo