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=-0.8 required=3.0 tests=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 CE092C3A589 for ; Thu, 15 Aug 2019 15:23:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A494F208C2 for ; Thu, 15 Aug 2019 15:23:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729082AbfHOPXZ (ORCPT ); Thu, 15 Aug 2019 11:23:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33402 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728846AbfHOPXZ (ORCPT ); Thu, 15 Aug 2019 11:23:25 -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 1A05CC06511D; Thu, 15 Aug 2019 15:23:25 +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 AF9E095A42; Thu, 15 Aug 2019 15:23:24 +0000 (UTC) Date: Thu, 15 Aug 2019 09:23:24 -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: <20190815092324.46bb3ac1@x1.home> In-Reply-To: <20190813201914.GI13991@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> <20190813115737.5db7d815@x1.home> <20190813133316.6fc6f257@x1.home> <20190813201914.GI13991@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 [10.5.110.31]); Thu, 15 Aug 2019 15:23:25 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, 13 Aug 2019 13:19:14 -0700 Sean Christopherson wrote: > On Tue, Aug 13, 2019 at 01:33:16PM -0600, Alex Williamson wrote: > > On Tue, 13 Aug 2019 11:57:37 -0600 > > Alex Williamson wrote: > > > Could it be something with the gfn test: > > > > if (sp->gfn != gfn) > > continue; > > > > If I remove it, I can't trigger the misbehavior. If I log it, I only > > get hits on VM boot/reboot and some of the gfns look suspiciously like > > they could be the assigned GPU BARs and maybe MSI mappings: > > > > (sp->gfn) != (gfn) > > Hits at boot/reboot makes sense, memslots get zapped when userspace > removes a memory region/slot, e.g. remaps BARs and whatnot. > > ... > > > Is this gfn optimization correct? Overzealous? Doesn't account > > correctly for something about MMIO mappings? Thanks, > > Yes? Shadow pages are stored in a hash table, for_each_valid_sp() walks > all entries for a given gfn. The sp->gfn check is there to skip entries > that hashed to the same list but for a completely different gfn. > > Skipping the gfn check would be sort of a lightweight zap all in the > sense that it would zap shadow pages that happend to collide with the > target memslot/gfn but are otherwise unrelated. > > What happens if you give just the GPU BAR at 0x80000000 a pass, i.e.: > > if (sp->gfn != gfn && sp->gfn != 0x80000) > continue; > > If that doesn't work, it might be worth trying other gfns to see if you > can pinpoint which sp is being zapped as collateral damage. > > It's possible there is a pre-existing bug somewhere else that was being > hidden because KVM was effectively zapping all SPTEs during (re)boot, > and the hash collision is also hiding the bug by zapping the stale entry. > > Of course it's also possible this code is wrong, :-) Ok, fun day of trying to figure out which ranges are relevant, I've narrowed it down to all of these: 0xffe00 0xfee00 0xfec00 0xc1000 0x80a000 0x800000 0x100000 ie. I can effective only say that sp->gfn values of 0x0, 0x40000, and 0x80000 can take the continue branch without seeing bad behavior in the VM. The assigned GPU has BARs at GPAs: 0xc0000000-0xc0ffffff 0x800000000-0x808000000 0x808000000-0x809ffffff And the assigned companion audio function is at GPA: 0xc1080000-0xc1083fff Only one of those seems to align very well with a gfn base involved here. The virtio ethernet has an mmio range at GPA 0x80a000000, otherwise I don't find any other I/O devices coincident with the gfns above. I'm running the VM with 2MB hugepages, but I believe the issue still occurs with standard pages. When run with standard pages I see more hits to gfn values 0, 0x40000, 0x80000, but the same number of hits to the set above that cannot take the continue branch. I don't know if that means anything. Any further ideas what to look for? Thanks, Alex PS - I see the posted workaround patch, I'll test that in the interim.