Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933133AbcK2RnZ (ORCPT ); Tue, 29 Nov 2016 12:43:25 -0500 Received: from mail-qt0-f177.google.com ([209.85.216.177]:36270 "EHLO mail-qt0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932646AbcK2RnP (ORCPT ); Tue, 29 Nov 2016 12:43:15 -0500 MIME-Version: 1.0 In-Reply-To: <1141665457.516897.1480406475749.JavaMail.zimbra@redhat.com> References: <1479863680-117511-1-git-send-email-dmatlack@google.com> <1479863680-117511-2-git-send-email-dmatlack@google.com> <1141665457.516897.1480406475749.JavaMail.zimbra@redhat.com> From: David Matlack Date: Tue, 29 Nov 2016 09:42:43 -0800 Message-ID: Subject: Re: [PATCH 1/4] KVM: nVMX: support restore of VMX capability MSRs To: Paolo Bonzini Cc: kvm list , "linux-kernel@vger.kernel.org" , Jim Mattson , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1829 Lines: 42 On Tue, Nov 29, 2016 at 12:01 AM, Paolo Bonzini wrote: >> On Mon, Nov 28, 2016 at 2:48 PM, Paolo Bonzini wrote: >> > On 28/11/2016 22:11, David Matlack wrote: >> >> > PINBASED_CTLS, PROCBASED_CTLS, EXIT_CTLS and ENTRY_CTLS can be derived >> >> > from their "true" counterparts, so I think it's better to remove the >> >> > "non-true" ones from struct nested_vmx (and/or add the "true" ones when >> >> > missing) and make them entirely computed. But it can be done on top. >> >> >> >> Good point. And that would mean userspace does not need to restore the >> >> non-true MSRs, right? >> > >> > Yes, sorry for being a bit too concise. :) >> >> I'll include this cleanup in the next version of the patchset since it >> affects which MSRs userspace will restore. It looks like a pretty >> simple patch. > > Don't bother removing the "non-true" registers from nested_vmx; you only > need to adjust the userspace API. I already wrote the patch, so unless there's an argument against removing them I'll include it in the next patchset. Thanks! > >> > >> >> KVM does not emulate MSR_IA32_VMX_BASIC[55]=0, >> >> and will probably never want to. >> > >> > That's a separate question, MSR_IA32_VMX_BASIC[55]=0 basically means >> > that the "true" capabilities are the same as the "default" capabilities. >> > If userspace wanted to set it that way, KVM right now would not hide >> > the "true" capability MSR, but on the other hand the nested hypervisor >> > should not even notice the difference. >> >> KVM would also need to use the non-true MSR in place of the true MSRs >> when checking VMCS12 during VM-entry. > > It's not necessary, userspace would set the relevant bits to 1 in the true > MSRs, for both the low and high parts. If it doesn't, it's garbage in > garbage out. > > Paolo