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,URIBL_BLOCKED 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 46DB3C34022 for ; Mon, 17 Feb 2020 15:39:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0CA3D208C4 for ; Mon, 17 Feb 2020 15:39:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OWDvIP3t" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729012AbgBQPjv (ORCPT ); Mon, 17 Feb 2020 10:39:51 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:60409 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726833AbgBQPjv (ORCPT ); Mon, 17 Feb 2020 10:39:51 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1581953990; 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=jKEw/9LD4IB/V5V6URoGZRoG+mly6ja1ybw5s5Rs0Gw=; b=OWDvIP3tjerM/Vbp7HMk9BKzBmC4C3XLPnCq3iRNBwczj7Vg1Cj32C782MfdPwoJA+XMKL 5bMLTbFjtNGIhpz2a9A/P8S791H+9jqyhW+DXo4zxYhgwht8FeEh9nO/gBnwsBp8ujnP3V POe6ILRjMdgMsLbzV8fRazLORMt8Wz0= 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-110-ILyhls4INymqfaQ-BGzzqQ-1; Mon, 17 Feb 2020 10:39:43 -0500 X-MC-Unique: ILyhls4INymqfaQ-BGzzqQ-1 Received: by mail-wr1-f72.google.com with SMTP id o9so9166886wrw.14 for ; Mon, 17 Feb 2020 07:39:42 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=jKEw/9LD4IB/V5V6URoGZRoG+mly6ja1ybw5s5Rs0Gw=; b=b/TDd3lyxicuD1l6kEUG1w7itgKDoz8oxTUcHPgkqhE3EhDgZpODvx5AG0LczZkbsG 9UgcYKFHzj7n4nclvZ+XiHZclVwes8mvdJZa9UAAAl/SPg5eWONNWfxxQpzt/XvezlzI p4isbtpRp3i0RyDeUM7ZeFLO4br/kDvt70XXfgmBETT2abXXnsWvb6nyOxeXcHs8ErWe hLBvPFBCriLk2LnrMYzITT21imwlWAhCFh0zdI7jALjrIKmKtBZ1wEE3p6DdZqFt5UAr xNJKS+O5VasPb6Bqd6RUOfW4Zrce3Qb9zPvk0/QraB/8jVczZQ9bIBz5d0Oab0fCw9qd sQ3w== X-Gm-Message-State: APjAAAVNlkIMCOlld4Y7Fr+rqHHsC6siuJGJGVIcDOmDp4YxEIyyh0IC HlbyYaQP05q+ljTJidKfjoJkYePH8oBeIiQQcbG7xl7ImJUZW4eX7KgM1fCQqPkIWYH1IqUYimq hdOdQFtRsEIkwqyvuupGbd6fi X-Received: by 2002:a1c:f009:: with SMTP id a9mr22758268wmb.73.1581953981725; Mon, 17 Feb 2020 07:39:41 -0800 (PST) X-Google-Smtp-Source: APXvYqw3F+p2TnTlGe9QutjrXQ9bs2FRZYLz6SXUgX3NY1Zh+sHedC61NY/0mD2N7zoHzN71kac2NA== X-Received: by 2002:a1c:f009:: with SMTP id a9mr22758229wmb.73.1581953981434; Mon, 17 Feb 2020 07:39:41 -0800 (PST) Received: from vitty.brq.redhat.com (nat-pool-brq-t.redhat.com. [213.175.37.10]) by smtp.gmail.com with ESMTPSA id x10sm1402119wrv.60.2020.02.17.07.39.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Feb 2020 07:39:40 -0800 (PST) From: Vitaly Kuznetsov To: Sean Christopherson , Peter Xu Cc: Paolo Bonzini , Paul Mackerras , Christian Borntraeger , Janosch Frank , David Hildenbrand , Cornelia Huck , Wanpeng Li , Jim Mattson , Joerg Roedel , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, Christoffer Dall , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH v5 15/19] KVM: Provide common implementation for generic dirty log functions In-Reply-To: <20200208012938.GC15581@linux.intel.com> References: <20200121223157.15263-1-sean.j.christopherson@intel.com> <20200121223157.15263-16-sean.j.christopherson@intel.com> <20200206200200.GC700495@xz-x1> <20200206212120.GF13067@linux.intel.com> <20200206214106.GG700495@xz-x1> <20200207194532.GK2401@linux.intel.com> <20200208001832.GA823968@xz-x1> <20200208004233.GA15581@linux.intel.com> <20200208005334.GB823968@xz-x1> <20200208012938.GC15581@linux.intel.com> Date: Mon, 17 Feb 2020 16:39:39 +0100 Message-ID: <87sgj99q9w.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sean Christopherson writes: > On Fri, Feb 07, 2020 at 07:53:34PM -0500, Peter Xu wrote: >> On Fri, Feb 07, 2020 at 04:42:33PM -0800, Sean Christopherson wrote: >> > On Fri, Feb 07, 2020 at 07:18:32PM -0500, Peter Xu wrote: >> > > On Fri, Feb 07, 2020 at 11:45:32AM -0800, Sean Christopherson wrote: >> > > > +Vitaly for HyperV >> > > > >> > > > On Thu, Feb 06, 2020 at 04:41:06PM -0500, Peter Xu wrote: >> > > > > On Thu, Feb 06, 2020 at 01:21:20PM -0800, Sean Christopherson wrote: >> > > > > > On Thu, Feb 06, 2020 at 03:02:00PM -0500, Peter Xu wrote: >> > > > > > > But that matters to this patch because if MIPS can use >> > > > > > > kvm_flush_remote_tlbs(), then we probably don't need this >> > > > > > > arch-specific hook any more and we can directly call >> > > > > > > kvm_flush_remote_tlbs() after sync dirty log when flush==true. >> > > > > > >> > > > > > Ya, the asid_flush_mask in kvm_vz_flush_shadow_all() is the only thing >> > > > > > that prevents calling kvm_flush_remote_tlbs() directly, but I have no >> > > > > > clue as to the important of that code. >> > > > > >> > > > > As said above I think the x86 lockdep is really not necessary, then >> > > > > considering MIPS could be the only one that will use the new hook >> > > > > introduced in this patch... Shall we figure that out first? >> > > > >> > > > So I prepped a follow-up patch to make kvm_arch_dirty_log_tlb_flush() a >> > > > MIPS-only hook and use kvm_flush_remote_tlbs() directly for arm and x86, >> > > > but then I realized x86 *has* a hook to do a precise remote TLB flush. >> > > > There's even an existing kvm_flush_remote_tlbs_with_address() call on a >> > > > memslot, i.e. this exact scenario. So arguably, x86 should be using the >> > > > more precise flush and should keep kvm_arch_dirty_log_tlb_flush(). >> > > > >> > > > But, the hook is only used when KVM is running as an L1 on top of HyperV, >> > > > and I assume dirty logging isn't used much, if at all, for L1 KVM on >> > > > HyperV? >> > > > >> > > > I see three options: >> > > > >> > > > 1. Make kvm_arch_dirty_log_tlb_flush() MIPS-only and call >> > > > kvm_flush_remote_tlbs() directly for arm and x86. Add comments to >> > > > explain when an arch should implement kvm_arch_dirty_log_tlb_flush(). >> > > > >> > > > 2. Change x86 to use kvm_flush_remote_tlbs_with_address() when flushing >> > > > a memslot after the dirty log is grabbed by userspace. >> > > > >> > > > 3. Keep the resulting code as is, but add a comment in x86's >> > > > kvm_arch_dirty_log_tlb_flush() to explain why it uses >> > > > kvm_flush_remote_tlbs() instead of the with_address() variant. >> > > > >> > > > I strongly prefer to (2) or (3), but I'll defer to Vitaly as to which of >> > > > those is preferable. >> > > > >> > > > I don't like (1) because (a) it requires more lines code (well comments), >> > > > to explain why kvm_flush_remote_tlbs() is the default, and (b) it would >> > > > require even more comments, which would be x86-specific in generic KVM, >> > > > to explain why x86 doesn't use its with_address() flush, or we'd lost that >> > > > info altogether. >> > > > >> > > >> > > I proposed the 4th solution here: >> > > >> > > https://lore.kernel.org/kvm/20200207223520.735523-1-peterx@redhat.com/ >> > > >> > > I'm not sure whether that's acceptable, but if it can, then we can >> > > drop the kvm_arch_dirty_log_tlb_flush() hook, or even move on to >> > > per-slot tlb flushing. >> > >> > This effectively is per-slot TLB flushing, it just has a different name. >> > I.e. s/kvm_arch_dirty_log_tlb_flush/kvm_arch_flush_remote_tlbs_memslot. >> > I'm not opposed to that name change. And on second and third glance, I >> > probably prefer it. That would more or less follow the naming of >> > kvm_arch_flush_shadow_all() and kvm_arch_flush_shadow_memslot(). >> >> Note that the major point of the above patchset is not about doing tlb >> flush per-memslot or globally. It's more about whether we can provide >> a common entrance for TLB flushing. Say, after that series, we should >> be able to flush TLB on all archs (majorly, including MIPS) as: >> >> kvm_flush_remote_tlbs(kvm); >> >> And with the same idea we can also introduce the ranged version. >> >> > >> > I don't want to go straight to kvm_arch_flush_remote_tlb_with_address() >> > because that loses the important distinction (on x86) that slots_lock is >> > expected to be held. >> >> Sorry I'm still puzzled on why that lockdep is so important and >> special for x86... For example, what if we move that lockdep to the >> callers of the kvm_arch_dirty_log_tlb_flush() calls so it protects >> even more arch (where we do get/clear dirty log)? IMHO the callers >> must be with the slots_lock held anyways no matter for x86 or not. > > > Following the breadcrumbs leads to the comment in > kvm_mmu_slot_remove_write_access(), which says: > > /* > * kvm_mmu_slot_remove_write_access() and kvm_vm_ioctl_get_dirty_log() > * which do tlb flush out of mmu-lock should be serialized by > * kvm->slots_lock otherwise tlb flush would be missed. > */ > > I.e. write-protecting a memslot and grabbing the dirty log for the memslot > need to be serialized. It's quite obvious *now* that get_dirty_log() holds > slots_lock, but the purpose of lockdep assertions isn't just to verify the > current functionality, it's to help ensure the correctness for future code > and to document assumptions in the code. > > Digging deeper, there are four functions, all related to dirty logging, in > the x86 mmu that basically open code what x86's > kvm_arch_flush_remote_tlbs_memslot() would look like if it uses the range > based flushing. > > Unless it's functionally incorrect (Vitaly?), going with option (2) and > naming the hook kvm_arch_flush_remote_tlbs_memslot() seems like the obvious > choice, e.g. the final cleanup gives this diff stat: (I apologize again for not replying in time) I think this is a valid approach and your option (2) would also be my choice. I also don't think there's going to be a problem when (if) Hyper-V adds support for PML (eVMCSv2?). > > arch/x86/kvm/mmu/mmu.c | 34 +++++++++------------------------- > 1 file changed, 9 insertions(+), 25 deletions(-) > Looks nice :-) -- Vitaly