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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 853E7C32750 for ; Tue, 13 Aug 2019 17:04:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 603252067D for ; Tue, 13 Aug 2019 17:04:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727144AbfHMREm (ORCPT ); Tue, 13 Aug 2019 13:04:42 -0400 Received: from mga11.intel.com ([192.55.52.93]:52516 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726993AbfHMREm (ORCPT ); Tue, 13 Aug 2019 13:04:42 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Aug 2019 10:04:41 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,382,1559545200"; d="scan'208";a="181243702" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by orsmga006.jf.intel.com with ESMTP; 13 Aug 2019 10:04:41 -0700 Date: Tue, 13 Aug 2019 10:04:41 -0700 From: Sean Christopherson To: Alex Williamson 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: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190813100458.70b7d82d@x1.home> 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 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. > 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); } > > Alex > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 24843cf49579..6a77306940f7 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -5653,6 +5653,9 @@ static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm, > struct kvm_memory_slot *slot, > struct kvm_page_track_notifier_node *node) > { > +#if 0 > + kvm_mmu_zap_all(kvm); > +#else > struct kvm_mmu_page *sp; > LIST_HEAD(invalid_list); > unsigned long i; > @@ -5685,6 +5688,7 @@ static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm, > > out_unlock: > spin_unlock(&kvm->mmu_lock); > +#endif > } > > void kvm_mmu_init_vm(struct kvm *kvm)