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=-4.6 required=3.0 tests=BAYES_00,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 636F6C4727D for ; Tue, 6 Oct 2020 17:28:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 139C920674 for ; Tue, 6 Oct 2020 17:28:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="evIwa8Wc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726469AbgJFR2n (ORCPT ); Tue, 6 Oct 2020 13:28:43 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:58497 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725902AbgJFR2l (ORCPT ); Tue, 6 Oct 2020 13:28:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1602005319; 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=wqrPuKYcvN3AHluRTjmmIKpi9e8SscqeWEpVovkcGa4=; b=evIwa8WcOrITSrFtHUcP8ioE+j9LUqgRJ/Fa4aj8MXmprmXcSMVNz5J1it1hSHHT4mJr8A x9eVbdT12vHQO7ID7lft0qJXA6tFilFrpKObBIxQsdjeYFvPe0b3Iidl37DMernq0EoEFv mULf1NGqnHSo/LrkT/tjtNDzKxm5u3Q= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-554-rK7lJLgJOw2-SXm9xxHDIQ-1; Tue, 06 Oct 2020 13:28:37 -0400 X-MC-Unique: rK7lJLgJOw2-SXm9xxHDIQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BC7CE108E1A1; Tue, 6 Oct 2020 17:28:36 +0000 (UTC) Received: from horse.redhat.com (ovpn-117-72.rdu2.redhat.com [10.10.117.72]) by smtp.corp.redhat.com (Postfix) with ESMTP id 69CA43A40; Tue, 6 Oct 2020 17:28:33 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id EDF21220AD7; Tue, 6 Oct 2020 13:28:32 -0400 (EDT) Date: Tue, 6 Oct 2020 13:28:32 -0400 From: Vivek Goyal To: "Dr. David Alan Gilbert" Cc: Sean Christopherson , Vitaly Kuznetsov , virtio-fs-list , pbonzini@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [Virtio-fs] [PATCH v4] kvm, x86: Exit to user space in case page fault error Message-ID: <20201006172832.GF5306@redhat.com> References: <20201006134629.GB5306@redhat.com> <877ds38n6r.fsf@vitty.brq.redhat.com> <20201006141501.GC5306@redhat.com> <874kn78l2z.fsf@vitty.brq.redhat.com> <20201006150817.GD5306@redhat.com> <871rib8ji1.fsf@vitty.brq.redhat.com> <20201006161200.GB17610@linux.intel.com> <87y2kj71gj.fsf@vitty.brq.redhat.com> <20201006171704.GC17610@linux.intel.com> <20201006172148.GI3000@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201006172148.GI3000@work-vm> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 06, 2020 at 06:21:48PM +0100, Dr. David Alan Gilbert wrote: > * Sean Christopherson (sean.j.christopherson@intel.com) wrote: > > On Tue, Oct 06, 2020 at 06:39:56PM +0200, Vitaly Kuznetsov wrote: > > > Sean Christopherson writes: > > > > > > > On Tue, Oct 06, 2020 at 05:24:54PM +0200, Vitaly Kuznetsov wrote: > > > >> Vivek Goyal writes: > > > >> > So you will have to report token (along with -EFAULT) to user space. So this > > > >> > is basically the 3rd proposal which is extension of kvm API and will > > > >> > report say HVA/GFN also to user space along with -EFAULT. > > > >> > > > >> Right, I meant to say that guest kernel has full register state of the > > > >> userspace process which caused APF to get queued and instead of trying > > > >> to extract it in KVM and pass to userspace in case of a (later) failure > > > >> we limit KVM api change to contain token or GFN only and somehow keep > > > >> the rest in the guest. This should help with TDX/SEV-ES. > > > > > > > > Whatever gets reported to userspace should be identical with and without > > > > async page faults, i.e. it definitely shouldn't have token information. > > > > > > > > > > Oh, right, when the error gets reported synchronously guest's kernel is > > > not yet aware of the issue so it won't be possible to find anything in > > > its kdump if userspace decides to crash it immediately. The register > > > state (if available) will be actual though. > > > > > > > Note, TDX doesn't allow injection exceptions, so reflecting a #PF back > > > > into the guest is not an option. > > > > > > Not even #MC? So sad :-) > > > > Heh, #MC isn't allowed either, yet... > > > > > > Nor do I think that's "correct" behavior (see everyone's objections to > > > > using #PF for APF fixed). I.e. the event should probably be an IRQ. > > > > > > I recall Paolo objected against making APF 'page not present' into in > > > interrupt as it will require some very special handling to make sure it > > > gets injected (and handled) immediately but I'm not really sure how big > > > the hack is going to be, maybe in the light of TDX/SEV-ES it's worth a > > > try. > > > > This shouldn't have anything to do with APF. Again, the event injection is > > needed even in the synchronous case as the file truncation in the host can > > affect existing mappings in the guest. > > > > I don't know that the mechanism needs to be virtiofs specific or if there can > > be a more generic "these PFNs have disappeared", but it's most definitely > > orthogonal to APF. > > There are other cases we get 'these PFNs have disappeared' other than > virtiofs; the classic is when people back the guest using a tmpfs that > then runs out of room. I also played with nvdimm driver where device was backed a file on host. If I truncate that file, we face similar issues. https://lore.kernel.org/kvm/20200616214847.24482-1-vgoyal@redhat.com/ I think any resource which can be backed by a file on host, can potentially run into this issue if file is truncated. (if guest can do load/store on these pages directly). Thanks Vivek