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=-3.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 2F029C3F2CD for ; Mon, 23 Mar 2020 16:26:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E5DCC20722 for ; Mon, 23 Mar 2020 16:26:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="iCCDAtZu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727406AbgCWQ01 (ORCPT ); Mon, 23 Mar 2020 12:26:27 -0400 Received: from us-smtp-delivery-74.mimecast.com ([216.205.24.74]:38776 "EHLO us-smtp-delivery-74.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727277AbgCWQ00 (ORCPT ); Mon, 23 Mar 2020 12:26:26 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1584980784; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Ehj56ajVRi23GK2T3VjArh7Mw9HqSg7LkHrp/uuAqAM=; b=iCCDAtZu1JQ6OJ118HCcY93NZVfuKGySfp5H4zlVtiEah+bjRIfmMf9NTMb48b2czBS6bs nCNuSOOtiJyP5zZ7wJj3z4na57cgzxUFEq1WpXrkhRbnGAGpkzOUZK2/Rm/l77f+A81L1b YO/BiUtdZXJi7VhZuJldmW/iYAum/Es= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-449-t_aCfB5MOkmVeqKev15yYA-1; Mon, 23 Mar 2020 12:26:23 -0400 X-MC-Unique: t_aCfB5MOkmVeqKev15yYA-1 Received: by mail-wr1-f72.google.com with SMTP id w12so987043wrl.23 for ; Mon, 23 Mar 2020 09:26:23 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=Ehj56ajVRi23GK2T3VjArh7Mw9HqSg7LkHrp/uuAqAM=; b=nHXNfNDYCoqkgulL8rR3eN1gptlOOiNtyU/OUG0CStKasA3GfohqjOgi2QsrXvv2/j GDow9ZWA06jSLcYX63PSWdpwJIq/INrM5TRfr0pgPbaY8HsO4S/kbYDZJXbcu+S7rZPn l8+Ft7h6bbJT7hzknalzZmTCuS2eL88WiBtG09yzpuwi5zwERz/jxXv5HvMn/s1vsCEZ tyMuCLpzJ6LGQLPpM9boN+uECcu3hwmGfUiFUVsaHuh+xPAQ1aUJlMt+ZtQ1R05ST+Nf OpsWP7jC5ztbmd90XqlAPG37Gm2Czea+c196l5Bt93gqIuQhHYg41X0b5q6I7QZfJ/pV xr8Q== X-Gm-Message-State: ANhLgQ1SirFc2CRizQLtWddf+mDohg6m9Jvb1/ibRlfsDyiLi1vnk8GJ XseHu2gwKh/oMR5Nhik1RuY8z7f6a2GmhDRa0WT8afc9fXN7GQcnMNz+GHFqNq7YMBFbmxidJbr bLeeKXf4eAbJa X-Received: by 2002:adf:edcf:: with SMTP id v15mr21828459wro.309.1584980782064; Mon, 23 Mar 2020 09:26:22 -0700 (PDT) X-Google-Smtp-Source: ADFU+vtMysjez2ebPBp50c+OTI7OG21qECbdMaArQCV37S+j+P83ACU6Rz9s2G4ofu1vahE6S+f0NQ== X-Received: by 2002:adf:edcf:: with SMTP id v15mr21828443wro.309.1584980781832; Mon, 23 Mar 2020 09:26:21 -0700 (PDT) Received: from xz-x1 ([2607:9880:19c0:32::2]) by smtp.gmail.com with ESMTPSA id a8sm66129wmb.39.2020.03.23.09.26.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Mar 2020 09:26:21 -0700 (PDT) Date: Mon, 23 Mar 2020 12:26:17 -0400 From: Peter Xu To: Sean Christopherson 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: <20200323162617.GK127076@xz-x1> References: <20200318163720.93929-1-peterx@redhat.com> <20200318163720.93929-4-peterx@redhat.com> <20200321192211.GC13851@linux.intel.com> <20200323145824.GI127076@xz-x1> <20200323154216.GG28711@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200323154216.GG28711@linux.intel.com> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Mar 23, 2020 at 08:42:16AM -0700, Sean Christopherson wrote: > 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. Yes I completely agree if you mean the pure mapping of GPA->HVA. I think it's a matter of how to define the "valid" when you say "guaranteed to remain valid", because I don't think the mapping is still valid from the most strict sense if e.g. the backing HVA does not exist any more for that GPA->HVA mapping, then the memslot won't be anything useful. > > > 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. I wanted to mean "the userspace unmaps the HVA" is not important. The mapping is for sure important! Thanks, -- Peter Xu