From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752935AbeBZMlp (ORCPT ); Mon, 26 Feb 2018 07:41:45 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:35438 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752698AbeBZMll (ORCPT ); Mon, 26 Feb 2018 07:41:41 -0500 Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version To: Borislav Petkov Cc: Wanpeng Li , LKML , kvm , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= References: <20180226111630.GB4377@pd.tnic> <20180226113000.GC4377@pd.tnic> <20180226114409.GD4377@pd.tnic> <46cecef2-b0fb-b0c2-bbf3-983328d52763@redhat.com> <20180226121509.GE4377@pd.tnic> <24cd527d-5287-f0be-ffe8-eab341bf1d94@redhat.com> <3866d359-0ef8-6a99-6254-84890be62b93@redhat.com> <20180226122205.GG4377@pd.tnic> From: Paolo Bonzini Message-ID: Date: Mon, 26 Feb 2018 13:41:38 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180226122205.GG4377@pd.tnic> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26/02/2018 13:22, Borislav Petkov wrote: > On Mon, Feb 26, 2018 at 01:18:07PM +0100, Paolo Bonzini wrote: >>> In this context, "host-initiated" write means written by KVM userspace >>> with ioctl(KVM_SET_MSR). It generally happens only on VM startup, reset >>> or live migration. >> >> To be clear, the target of the write is still the vCPU's emulated MSR. > > So how am I to imagine this as a user: > > qemu-system-x86_64 --microcode-revision=0xdeadbeef... More like "-cpu foo,ucode_rev=0xdeadbeef". But in practice what would happen is one of the following: 1) "-cpu host" sets ucode_rev to the same value of the host, everyone else leaves it to zero as is now. 2) Only Amazon uses this feature and we ignore it. :) Paolo