From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: Should KVM_GUEST stop depending on PARAVIRT? Date: Mon, 27 Jul 2015 15:59:15 +0200 Message-ID: <55B63933.4090702@redhat.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit To: Andy Lutomirski , KVM list Return-path: Received: from mail-wi0-f171.google.com ([209.85.212.171]:38562 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752992AbbG0N7R (ORCPT ); Mon, 27 Jul 2015 09:59:17 -0400 Received: by wibxm9 with SMTP id xm9so118098663wib.1 for ; Mon, 27 Jul 2015 06:59:16 -0700 (PDT) In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 24/07/2015 19:33, Andy Lutomirski wrote: > PARAVIRT adds a fair amount of bloat and, AFAICT, KVM_GUEST doesn't > really need any of it. Would it make sense to drop the dependency? I think the main reason for PARAVIRT is that pv kernels have by default .read_msr = native_read_msr_safe, .write_msr = native_write_msr_safe, Unfortunately Intel adds a bunch of performance measurement features saying that "they work with this cpuid family/model/stepping" and at the same time attach them to some non-architectural MSRs that, in principle could be reused for something else years down the road. This is not a huge problem for Windows, where only tools such as vTune use these MSRs, but it is a problem for Linux. The alternative is ignore_msrs, but that's a very big hammer too. Paolo