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=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,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 99D13C4363A for ; Thu, 8 Oct 2020 10:54:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 381F92177B for ; Thu, 8 Oct 2020 10:54:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="RYaeYYaD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729637AbgJHKyL (ORCPT ); Thu, 8 Oct 2020 06:54:11 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:57944 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726029AbgJHKyL (ORCPT ); Thu, 8 Oct 2020 06:54:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1602154449; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=f8QBV41rmQgiRf1XN5VQfdRosA8a5M4RouzGU9oT7BI=; b=RYaeYYaD5G0N7owDMFi/TDKJi2lmKOmrOVRfwL5DpmAnJjPDPTSB8L4Tl11QiuRsB6WlaB VARO/HP2sGOf3zUfoY4d4IUyqeU5P+ZKF6YxbnjZr5QXX50A1+n13bmDqJrnMs8qWM6K09 twOZNkKBeJ6PuZftzUpegijth89EdFU= 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-298-mWV7QnvbNCGYnkkqVy2Z3A-1; Thu, 08 Oct 2020 06:54:07 -0400 X-MC-Unique: mWV7QnvbNCGYnkkqVy2Z3A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F2CA6804018; Thu, 8 Oct 2020 10:54:05 +0000 (UTC) Received: from starship (unknown [10.35.206.84]) by smtp.corp.redhat.com (Postfix) with ESMTP id 751ED6EF5F; Thu, 8 Oct 2020 10:54:01 +0000 (UTC) Message-ID: <51d447be4a6f430ed5cc60242457394aceb004e9.camel@redhat.com> Subject: Re: [PATCH] KVM: SVM: Use a separate vmcb for the nested L2 guest From: Maxim Levitsky To: Paolo Bonzini , Cathy Avery , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: vkuznets@redhat.com, wei.huang2@amd.com Date: Thu, 08 Oct 2020 13:54:00 +0300 In-Reply-To: References: <20200917192306.2080-1-cavery@redhat.com> <587d1da1a037dd3ab7844c5cacc50bfda5ce6021.camel@redhat.com> <0007205290de75f04f5f2a92b891815438fd2f2f.camel@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.3 (3.36.3-1.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2020-10-08 at 13:39 +0300, Maxim Levitsky wrote: > On Thu, 2020-10-08 at 13:23 +0300, Maxim Levitsky wrote: > > On Thu, 2020-10-08 at 07:52 +0200, Paolo Bonzini wrote: > > > On 08/10/20 00:14, Maxim Levitsky wrote: > > > > > + if (svm->vmcb01->control.asid == 0) > > > > > + svm->vmcb01->control.asid = svm->nested.vmcb02->control.asid; > > > > > > > > I think that the above should be done always. The asid field is currently host > > > > controlled only (that is L2 value is ignored, selective ASID tlb flush is not > > > > advertized to the guest and lnvlpga is emulated as invlpg). > > > > > > Yes, in fact I suggested that ASID should be in svm->asid and moved to > > > svm->vmcb->asid in svm_vcpu_run. Then there's no need to special case > > > it in nested code. > > This makes lot of sense! > > > This should be a patch coming before this one. > > > > > > > 1. Something wrong with memory types - like guest is using UC memory for everything. > > > > I can't completely rule that out yet > > > > > > You can print g_pat and see if it is all zeroes. > > I don't even need to print it. I know that it is never set anywhere, unless guest writes it, > > but now that I look at it, we set it to a default value and there is no code to set it to > > default value for vmcb02. This is it. now my fedora guest boots just fine! > > > > I played a lot with g_pat, and yet this didn't occur to me . I was that close :-( > > I knew that it has to be something with memory types, but it never occured to me > > that guest just doesn't write IA32_PAT and uses our value which we set in init_vmcb > > > > > > > In general I think it's better to be explicit with vmcb01 vs. vmcb02, > > > like Cathy did, but I can see it's a matter of personal preference to > > > some extent. > > I also think so in general, but in the code that is outside 'is_guest_mode' > > IMHO it is better to refer to vmcb01 as vmcb, although now that I think of > > it, its not wrong to do so either. > > > > > > My windows hyper-v guest doesn't boot though and I know why. > > > > As we know the vmcb save area has extra state which vmrun/vmexit don't touch. > > Now suppose a nested hypervisor wants to enter a nested guest. > > > > It will do vmload, which will load the extra state from the nested vmcb (vmcb12 > > or as I woudl say the vmcb that nested hypervisor thinks that it is using), > > to the CPU. This can cause some vmexits I think, but this doesn't matter much. > > > > Now the nested hypervisor does vmrun. The extra state of L2 guest is in CPU registers, > > and it is untouched. We do vmsave on vmcb01 to preserve that state, but later > > when we do vmload on vmcb02 prior to vmenter on it, which loads stale state from it. > > The same issue happens the other way around on nested vmexit. > > > > I fixed this by doing nested_svm_vmloadsave, but that should be probably be > > optimized with dirty bits. Now though I guess the goal it to make > > it work first. > > > > With this fixed HyperV boots fine, and even passes the 'works' test of booting > > the windows 10 with hyperv enabled nested itself and starting the vm inside, > > which makes that VM L3 (in addition to windows itself that runs as L3 in relation to hyper-v) > > > > https://i.imgur.com/sRYqtVV.png > > > > In summary this is the diff of fixes (just pasted to email, probably mangled): > > > > > > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c > > index 0a06e62010d8c..7293ba23b3cbc 100644 > > --- a/arch/x86/kvm/svm/nested.c > > +++ b/arch/x86/kvm/svm/nested.c > > @@ -436,6 +436,9 @@ int enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa, > > WARN_ON(svm->vmcb == svm->nested.vmcb02); > > > > svm->nested.vmcb02->control = svm->vmcb01->control; > > + > > + nested_svm_vmloadsave(svm->vmcb01, svm->nested.vmcb02); > > + > > svm->vmcb = svm->nested.vmcb02; > > svm->vmcb_pa = svm->nested.vmcb02_pa; > > load_nested_vmcb_control(svm, &nested_vmcb->control); > > @@ -622,6 +625,7 @@ int nested_svm_vmexit(struct vcpu_svm *svm) > > if (svm->vmcb01->control.asid == 0) > > svm->vmcb01->control.asid = svm->nested.vmcb02->control.asid; > > > > + nested_svm_vmloadsave(svm->nested.vmcb02, svm->vmcb01); > > svm->vmcb = svm->vmcb01; > > svm->vmcb_pa = svm->nested.vmcb01_pa; > > > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > > index b66239b26885d..ee9f87fe611f2 100644 > > --- a/arch/x86/kvm/svm/svm.c > > +++ b/arch/x86/kvm/svm/svm.c > > @@ -1097,6 +1097,7 @@ static void init_vmcb(struct vcpu_svm *svm) > > clr_cr_intercept(svm, INTERCEPT_CR3_READ); > > clr_cr_intercept(svm, INTERCEPT_CR3_WRITE); > > save->g_pat = svm->vcpu.arch.pat; > > + svm->nested.vmcb02->save.g_pat = svm->vcpu.arch.pat; > > save->cr3 = 0; > > save->cr4 = 0; > > } > > > > > > > > Best regards, > > Maxim Levitsky > > > > > Paolo > > > > And another thing I spotted before I forget. > > If we setup a tlb flush in ctl.tlb_ctl of vmcb01, just prior to nested vmentry > then this field will be copied to vmcb02 but on next vmexit we clear it in current > (that is vmcb02) and that change will not propogate to vmcb01. > > I am not sure if this is a theorerical issue or not. We probably should apply the same treatment to > it as what Paulo suggested to do with asid - > set it just prior to vmentry if tlb flush is needed, and clear it afterwards as we do. And yet another thing to note is that we curently ignore L2's g_pat. However it _seems_ that we practically ignore L1 PAT as well in regard to shadowing NPT mmu. I am not 100% sure about this. I'll dig that area eventually. Best regards, Maxim Levitsky > > Best regards, > Maxim Levitsky