From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp2120.oracle.com ([141.146.126.78]:55956 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751351AbeBWRz7 (ORCPT ); Fri, 23 Feb 2018 12:55:59 -0500 Date: Fri, 23 Feb 2018 12:55:43 -0500 From: Konrad Rzeszutek Wilk To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org, Radim =?utf-8?B?S3LEjW3DocWZ?= , KarimAllah Ahmed , David Woodhouse , Jim Mattson , Thomas Gleixner , Ingo Molnar , stable@vger.kernel.org Subject: Re: [PATCH 1/3] KVM: x86: use native MSR ops for SPEC_CTRL Message-ID: <20180223175543.GN8252@char.us.oracle.com> References: <1519249297-73718-1-git-send-email-pbonzini@redhat.com> <1519249297-73718-2-git-send-email-pbonzini@redhat.com> <20180222170717.GP31483@char.us.oracle.com> <20180223172220.GK8252@char.us.oracle.com> <7534bcd3-e21b-240c-9ed2-62026ba10301@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7534bcd3-e21b-240c-9ed2-62026ba10301@redhat.com> Sender: stable-owner@vger.kernel.org List-ID: On Fri, Feb 23, 2018 at 06:35:30PM +0100, Paolo Bonzini wrote: > On 23/02/2018 18:22, Konrad Rzeszutek Wilk wrote: > > On Fri, Feb 23, 2018 at 10:37:49AM +0100, Paolo Bonzini wrote: > >> On 22/02/2018 18:07, Konrad Rzeszutek Wilk wrote: > >>>> Having a paravirt indirect call in the IBRS restore path is not a > >>>> good idea, since we are trying to protect from speculative execution > >>>> of bogus indirect branch targets. It is also slower, so use > >>>> native_wrmsrl on the vmentry path too. > >>> But it gets replaced during patching. As in once the machine boots > >>> the assembler changes from: > >>> > >>> callq *0xfffflbah > >>> > >>> to > >>> wrmsr > >>> > >>> ? I don't think you need this patch. > >> > >> Why not be explicit? According to the spec, PRED_CMD and SPEC_CTRL > > > > Explicit is fine. > > > > But I would recommend you change the commit message to say so, and > > perhaps remove 'It is also slower' - as that is incorrect. > > Actually it is faster---that's why I made the change in the first place, > though later I noticed > > > If it is detected to be Xen PV, then yes > > it will be a call to a function. But that won't help as Xen PV runs in > > ring 3, so it has a whole bunch of other issues. > > Ok, I wasn't sure about PVH (which runs in ring 0 afair). Right. PVH is HVM without any emulated devices or BIOSes or such. In the context of the paravirt ops, Xen PVH == Xen HVM. Xen PV (and lguests) are the only ones that patch the the callq *0xffffblah to callq 0xffff800 While everyone else does the wrmsr. > > Paolo