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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 D3228C2D0DB for ; Fri, 31 Jan 2020 20:36:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AF81D20707 for ; Fri, 31 Jan 2020 20:36:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726138AbgAaUgX (ORCPT ); Fri, 31 Jan 2020 15:36:23 -0500 Received: from mga07.intel.com ([134.134.136.100]:10439 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726074AbgAaUgX (ORCPT ); Fri, 31 Jan 2020 15:36:23 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 31 Jan 2020 12:36:22 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,387,1574150400"; d="scan'208";a="247838310" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga002.jf.intel.com with ESMTP; 31 Jan 2020 12:36:22 -0800 Date: Fri, 31 Jan 2020 12:36:22 -0800 From: Sean Christopherson To: Peter Xu Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Christophe de Dinechin , "Michael S . Tsirkin" , Paolo Bonzini , Yan Zhao , Alex Williamson , Jason Wang , Kevin Kevin , Vitaly Kuznetsov , "Dr . David Alan Gilbert" Subject: Re: [PATCH v3 09/21] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR] Message-ID: <20200131203622.GF18946@linux.intel.com> References: <20200109145729.32898-1-peterx@redhat.com> <20200109145729.32898-10-peterx@redhat.com> <20200121155657.GA7923@linux.intel.com> <20200128055005.GB662081@xz-x1> <20200128182402.GA18652@linux.intel.com> <20200131150832.GA740148@xz-x1> <20200131193301.GC18946@linux.intel.com> <20200131202824.GA7063@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200131202824.GA7063@xz-x1> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, Jan 31, 2020 at 03:28:24PM -0500, Peter Xu wrote: > On Fri, Jan 31, 2020 at 11:33:01AM -0800, Sean Christopherson wrote: > > For the same reason we don't take mmap_sem, it gains us nothing, i.e. KVM > > still has to use copy_{to,from}_user(). > > > > In the proposed __x86_set_memory_region() refactor, vmx_set_tss_addr() > > would be provided the hva of the memory region. Since slots_lock and SRCU > > only protect gfn->hva, why would KVM take slots_lock since it already has > > the hva? > > OK so you're suggesting to unlock the lock earlier to not cover > init_rmode_tss() rather than dropping the whole lock... Yes it looks > good to me. I think that's the major confusion I got. Ya. And I missed where the -EEXIST was coming from. I think we're on the same page. > > Returning -EEXIST is an ABI change, e.g. userspace can currently call > > KVM_SET_TSS_ADDR any number of times, it just needs to ensure proper > > serialization between calls. > > > > If you want to change the ABI, then submit a patch to do exactly that. > > But don't bury an ABI change under the pretense that it's a bug fix. > > Could you explain what do you mean by "ABI change"? > > I was talking about the original code, not after applying the > patchset. To be explicit, I mean [a] below: > > int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size, > unsigned long *uaddr) > { > int i, r; > unsigned long hva; > struct kvm_memslots *slots = kvm_memslots(kvm); > struct kvm_memory_slot *slot, old; > > /* Called with kvm->slots_lock held. */ > if (WARN_ON(id >= KVM_MEM_SLOTS_NUM)) > return -EINVAL; > > slot = id_to_memslot(slots, id); > if (size) { > if (slot->npages) > return -EEXIST; <------------------------ [a] > } > ... > } Doh, I completely forgot that the second __x86_set_memory_region() would fail. Sorry :-( > > > Yes, but as I mentioned, I don't think it's an issue to be considered > > > by KVM, otherwise we should have the same issue all over the places > > > when we fetch the cached userspace_addr from any user slots. > > > > Huh? Of course it's an issue that needs to be considered by KVM, e.g. > > kvm_{read,write}_guest_cached() aren't using __copy_{to,}from_user() for > > giggles. > > The cache is for the GPA->HVA translation (struct gfn_to_hva_cache), > we still use __copy_{to,}from_user() upon the HVAs, no? I'm still lost on this one. I'm pretty sure I'm incorrectly interpreting: I don't think it's an issue to be considered by KVM, otherwise we should have the same issue all over the places when we fetch the cached userspace_addr from any user slots. What is the issue to which you are referring?