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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 2479BC2D0CD for ; Tue, 17 Dec 2019 16:18:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E173021835 for ; Tue, 17 Dec 2019 16:18:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="HZbZ2275" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729393AbfLQQSt (ORCPT ); Tue, 17 Dec 2019 11:18:49 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:28410 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729069AbfLQQSt (ORCPT ); Tue, 17 Dec 2019 11:18:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1576599526; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=vK5NDcBxim7yNbmFnJiOrQ1gwFPi/J/vE1JJF/ionzc=; b=HZbZ22750qr61IBA33Ps03ASUNsRAUZc72HiDowOpMNCfK9XmPYFDc4hcUgXys9Gra1aAX cdGzFs9WoJ/Cl6od1px0Z4H/6jgiew2KjNegR+VzxcQLJi5QyqEBKZKujbVYUZJPdENoj1 REHyGUDYAG3VUvO91ib66JbBusBiHqc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-246-AFz6fOSUM3alHFfb2t83Tg-1; Tue, 17 Dec 2019 11:18:42 -0500 X-MC-Unique: AFz6fOSUM3alHFfb2t83Tg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9E8DF800D24; Tue, 17 Dec 2019 16:18:41 +0000 (UTC) Received: from x1.home (ovpn-116-53.phx2.redhat.com [10.3.116.53]) by smtp.corp.redhat.com (Postfix) with ESMTP id 83C2F68872; Tue, 17 Dec 2019 16:18:38 +0000 (UTC) Date: Tue, 17 Dec 2019 09:18:37 -0700 From: Alex Williamson To: "Tian, Kevin" Cc: Paolo Bonzini , Peter Xu , "Christopherson, Sean J" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "Dr . David Alan Gilbert" , Vitaly Kuznetsov , "Wang, Zhenyu Z" , "Zhao, Yan Y" Subject: Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking Message-ID: <20191217091837.744982d3@x1.home> In-Reply-To: References: <20191202201036.GJ4063@linux.intel.com> <20191202211640.GF31681@xz-x1> <20191202215049.GB8120@linux.intel.com> <20191203184600.GB19877@linux.intel.com> <374f18f1-0592-9b70-adbb-0a72cc77d426@redhat.com> <20191209215400.GA3352@xz-x1> <20191210155259.GD3352@xz-x1> <3e6cb5ec-66c0-00ab-b75e-ad2beb1d216d@redhat.com> <20191215172124.GA83861@xz-x1> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, 17 Dec 2019 02:28:33 +0000 "Tian, Kevin" wrote: > > From: Paolo Bonzini > > Sent: Monday, December 16, 2019 6:08 PM > > > > [Alex and Kevin: there are doubts below regarding dirty page tracking > > from VFIO and mdev devices, which perhaps you can help with] > > > > On 15/12/19 18:21, Peter Xu wrote: > > > init_rmode_tss > > > vmx_set_tss_addr > > > kvm_vm_ioctl_set_tss_addr [*] > > > init_rmode_identity_map > > > vmx_create_vcpu [*] > > > > These don't matter because their content is not visible to userspace > > (the backing storage is mmap-ed by __x86_set_memory_region). In fact, d > > > > > vmx_write_pml_buffer > > > kvm_arch_write_log_dirty [&] > > > kvm_write_guest > > > kvm_hv_setup_tsc_page > > > kvm_guest_time_update [&] > > > nested_flush_cached_shadow_vmcs12 [&] > > > kvm_write_wall_clock [&] > > > kvm_pv_clock_pairing [&] > > > kvmgt_rw_gpa [?] > > > > This then expands (partially) to > > > > intel_gvt_hypervisor_write_gpa > > emulate_csb_update > > emulate_execlist_ctx_schedule_out > > complete_execlist_workload > > complete_current_workload > > workload_thread > > emulate_execlist_ctx_schedule_in > > prepare_execlist_workload > > prepare_workload > > dispatch_workload > > workload_thread > > > > So KVMGT is always writing to GPAs instead of IOVAs and basically > > bypassing a guest IOMMU. So here it would be better if kvmgt was > > changed not use kvm_write_guest (also because I'd probably have nacked > > that if I had known :)). > > I agree. > > > > > As far as I know, there is some work on live migration with both VFIO > > and mdev, and that probably includes some dirty page tracking API. > > kvmgt could switch to that API, or there could be VFIO APIs similar to > > kvm_write_guest but taking IOVAs instead of GPAs. Advantage: this would > > fix the GPA/IOVA confusion. Disadvantage: userspace would lose the > > tracking of writes from mdev devices. Kevin, are these writes used in > > any way? Do the calls to intel_gvt_hypervisor_write_gpa covers all > > writes from kvmgt vGPUs, or can the hardware write to memory as well > > (which would be my guess if I didn't know anything about kvmgt, which I > > pretty much don't)? > > intel_gvt_hypervisor_write_gpa covers all writes due to software mediation. > > for hardware updates, it needs be mapped in IOMMU through vfio_pin_pages > before any DMA happens. The ongoing dirty tracking effort in VFIO will take > every pinned page through that API as dirtied. > > However, currently VFIO doesn't implement any vfio_read/write_guest > interface yet. and it doesn't make sense to use vfio_pin_pages for software > dirtied pages, as pin is unnecessary and heavy involving iommu invalidation. > > Alex, if you are OK we'll work on such interface and move kvmgt to use it. > After it's accepted, we can also mark pages dirty through this new interface > in Kirti's dirty page tracking series. I'm not sure what you're asking for, is it an interface for the host CPU to read/write the memory backing of a mapped IOVA range without pinning pages? That seems like something like that would make sense for an emulation model where a page does not need to be pinned for physical DMA. If you're asking more for an interface that understands the userspace driver is a VM (ie. implied using a _guest postfix on the function name) and knows about GPA mappings beyond the windows directly mapped for device access, I'd not look fondly on such a request. Thanks, Alex