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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D11FFC3F2CD for ; Mon, 23 Mar 2020 15:42:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AE65E20409 for ; Mon, 23 Mar 2020 15:42:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727421AbgCWPmS (ORCPT ); Mon, 23 Mar 2020 11:42:18 -0400 Received: from mga02.intel.com ([134.134.136.20]:30555 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727389AbgCWPmS (ORCPT ); Mon, 23 Mar 2020 11:42:18 -0400 IronPort-SDR: NM4VjdK2iMCWrP2Fsi3492YkWv83ukvKmKYbb+peY/nOS/4BdY1i1L7f112k7S1c2Rm3blIDEZ Aby48UkdxAPg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Mar 2020 08:42:17 -0700 IronPort-SDR: +ids7V//oUP2Cg9ZK/lGG9GXZcBrYFVISXehY99PjtBSEXzqTBFsjQ0F/0+Ygpc5YdPQeMHIuM uc5K0RM/INug== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,296,1580803200"; d="scan'208";a="445854315" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by fmsmga005.fm.intel.com with ESMTP; 23 Mar 2020 08:42:16 -0700 Date: Mon, 23 Mar 2020 08:42:16 -0700 From: Sean Christopherson To: Peter Xu Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, "Michael S . Tsirkin" , Vitaly Kuznetsov , Yan Zhao , "Dr . David Alan Gilbert" , Christophe de Dinechin , Alex Williamson , Jason Wang , Kevin Tian , Paolo Bonzini Subject: Re: [PATCH v7 03/14] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR] Message-ID: <20200323154216.GG28711@linux.intel.com> References: <20200318163720.93929-1-peterx@redhat.com> <20200318163720.93929-4-peterx@redhat.com> <20200321192211.GC13851@linux.intel.com> <20200323145824.GI127076@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200323145824.GI127076@xz-x1> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 23, 2020 at 10:58:24AM -0400, Peter Xu wrote: > On Sat, Mar 21, 2020 at 12:22:11PM -0700, Sean Christopherson wrote: > > On Wed, Mar 18, 2020 at 12:37:09PM -0400, Peter Xu wrote: > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > > index e54c6ad628a8..a5123a0aa7d6 100644 > > > --- a/arch/x86/kvm/x86.c > > > +++ b/arch/x86/kvm/x86.c > > > @@ -9786,7 +9786,34 @@ void kvm_arch_sync_events(struct kvm *kvm) > > > kvm_free_pit(kvm); > > > } > > > > > > -int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) > > > +#define ERR_PTR_USR(e) ((void __user *)ERR_PTR(e)) > > > + > > > +/** > > > + * __x86_set_memory_region: Setup KVM internal memory slot > > > + * > > > + * @kvm: the kvm pointer to the VM. > > > + * @id: the slot ID to setup. > > > + * @gpa: the GPA to install the slot (unused when @size == 0). > > > + * @size: the size of the slot. Set to zero to uninstall a slot. > > > + * > > > + * This function helps to setup a KVM internal memory slot. Specify > > > + * @size > 0 to install a new slot, while @size == 0 to uninstall a > > > + * slot. The return code can be one of the following: > > > + * > > > + * HVA: on success (uninstall will return a bogus HVA) > > > + * -errno: on error > > > + * > > > + * The caller should always use IS_ERR() to check the return value > > > + * before use. NOTE: KVM internal memory slots are guaranteed and > > > > "are guaranteed" to ... > > > > > + * won't change until the VM is destroyed. This is also true to the > > > + * returned HVA when installing a new memory slot. The HVA can be > > > + * invalidated by either an errornous userspace program or a VM under > > > + * destruction, however as long as we use __copy_{to|from}_user() > > > + * properly upon the HVAs and handle the failure paths always then > > > + * we're safe. > > > > Regarding the HVA, it's a bit confusing saying that it's guaranteed to be > > valid, and then contradicting that in the second clause. Maybe something > > like this to explain the GPA->HVA is guaranteed to be valid, but the > > HVA->HPA is not. > > > > /* > > * before use. Note, KVM internal memory slots are guaranteed to remain valid > > * and unchanged until the VM is destroyed, i.e. the GPA->HVA translation will > > * not change. However, the HVA is a user address, i.e. its accessibility is > > * not guaranteed, and must be accessed via __copy_{to,from}_user(). > > */ > > Sure I can switch to this, though note that I still think the GPA->HVA > is not guaranteed logically because the userspace can unmap any HVA it > wants.. You're conflating the GPA->HVA translation with the validity of the HVA, i.e. the HVA->HPA and/or HVA->VMA translation/association. GPA->HVA is guaranteed because userspace doesn't have access to the memslot which defines that transation. > However I agree that shouldn't be important from kvm's perspective as long as > we always emphasize on using legal HVA accessors. The fact that GPA->HVA can't change _is_ important, otherwise KVM would need to take steps to ensure that whatever can change GPA->HVA can't run concurrently with consuming the HVA.