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 40818C3F68F for ; Sat, 8 Feb 2020 00:42:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 208FE22464 for ; Sat, 8 Feb 2020 00:42:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727387AbgBHAmh (ORCPT ); Fri, 7 Feb 2020 19:42:37 -0500 Received: from mga07.intel.com ([134.134.136.100]:61094 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727048AbgBHAmg (ORCPT ); Fri, 7 Feb 2020 19:42:36 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Feb 2020 16:42:35 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,415,1574150400"; d="scan'208";a="346332007" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by fmsmga001.fm.intel.com with ESMTP; 07 Feb 2020 16:42:34 -0800 Date: Fri, 7 Feb 2020 16:42:33 -0800 From: Sean Christopherson To: Peter Xu Cc: Vitaly Kuznetsov , 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 =?iso-8859-1?Q?Mathieu-Daud=E9?= Subject: Re: [PATCH v5 15/19] KVM: Provide common implementation for generic dirty log functions Message-ID: <20200208004233.GA15581@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200208001832.GA823968@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 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(). 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.