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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 525C4C433FF for ; Tue, 13 Aug 2019 17:57:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3312C2064A for ; Tue, 13 Aug 2019 17:57:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727844AbfHMR5j (ORCPT ); Tue, 13 Aug 2019 13:57:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39004 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725923AbfHMR5j (ORCPT ); Tue, 13 Aug 2019 13:57:39 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 7591013A82; Tue, 13 Aug 2019 17:57:38 +0000 (UTC) Received: from x1.home (ovpn-116-99.phx2.redhat.com [10.3.116.99]) by smtp.corp.redhat.com (Postfix) with ESMTP id 10D6ABA54; Tue, 13 Aug 2019 17:57:38 +0000 (UTC) Date: Tue, 13 Aug 2019 11:57:37 -0600 From: Alex Williamson To: Sean Christopherson Cc: Paolo Bonzini , Radim =?UTF-8?B?S3LEjW3DocWZ?= , kvm@vger.kernel.org, Xiao Guangrong Subject: Re: [PATCH v2 11/27] KVM: x86/mmu: Zap only the relevant pages when removing a memslot Message-ID: <20190813115737.5db7d815@x1.home> In-Reply-To: <20190813170440.GC13991@linux.intel.com> References: <20190205205443.1059-1-sean.j.christopherson@intel.com> <20190205210137.1377-11-sean.j.christopherson@intel.com> <20190813100458.70b7d82d@x1.home> <20190813170440.GC13991@linux.intel.com> 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 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Tue, 13 Aug 2019 17:57:38 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, 13 Aug 2019 10:04:41 -0700 Sean Christopherson wrote: > On Tue, Aug 13, 2019 at 10:04:58AM -0600, Alex Williamson wrote: > > On Tue, 5 Feb 2019 13:01:21 -0800 > > Sean Christopherson wrote: > > > > > Modify kvm_mmu_invalidate_zap_pages_in_memslot(), a.k.a. the x86 MMU's > > > handler for kvm_arch_flush_shadow_memslot(), to zap only the pages/PTEs > > > that actually belong to the memslot being removed. This improves > > > performance, especially why the deleted memslot has only a few shadow > > > entries, or even no entries. E.g. a microbenchmark to access regular > > > memory while concurrently reading PCI ROM to trigger memslot deletion > > > showed a 5% improvement in throughput. > > > > > > Cc: Xiao Guangrong > > > Signed-off-by: Sean Christopherson > > > --- > > > arch/x86/kvm/mmu.c | 33 ++++++++++++++++++++++++++++++++- > > > 1 file changed, 32 insertions(+), 1 deletion(-) > > > > A number of vfio users are reporting VM instability issues since v5.1, > > some have traced it back to this commit 4e103134b862 ("KVM: x86/mmu: Zap > > only the relevant pages when removing a memslot"), which I've confirmed > > via bisection of the 5.1 merge window KVM pull (636deed6c0bc) and > > re-verified on current 5.3-rc4 using the below patch to toggle the > > broken behavior. > > > > My reproducer is a Windows 10 VM with assigned GeForce GPU running a > > variety of tests, including FurMark and PassMark Performance Test. > > With the code enabled as exists in upstream currently, PassMark will > > generally introduce graphics glitches or hangs. Sometimes it's > > necessary to reboot the VM to see these issues. > > As in, the issue only shows up when the VM is rebooted? Just want to > double check that that's not a typo. No, it can occur on the first boot as well, it's just that the recipe to induce a failure is not well understood and manifests itself in different ways. I generally run the tests, then if it still hasn't reproduced, I reboot the VM a couple times, running a couple apps in between to try to trigger/notice bad behavior. > > Flipping the 0/1 in the below patch appears to resolve the issue. > > > > I'd appreciate any insights into further debugging this block of code > > so that we can fix this regression. Thanks, > > If it's not too painful to reproduce, I'd say start by determining whether > it's a problem with the basic logic or if the cond_resched_lock() handling > is wrong. I.e. comment/ifdef out this chunk: > > if (need_resched() || spin_needbreak(&kvm->mmu_lock)) { > kvm_mmu_remote_flush_or_zap(kvm, &invalid_list, flush); > flush = false; > cond_resched_lock(&kvm->mmu_lock); > } If anything, removing this chunk seems to make things worse. Thanks, Alex