From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: Re: rdmsr_safe in Linux PV (under Xen) gets an #GP:Re: [Fedora-xen] Running fedora xen on top of KVM? Date: Fri, 18 Sep 2015 08:20:46 -0700 Message-ID: References: <55F87984.7030903@redhat.com> <55F9C792.8070205@redhat.com> <55F9D95F.9040401@redhat.com> <20150916210814.GA4643@l.oracle.com> <55F9EF87.7030407@redhat.com> <20150917201053.GB12745@l.oracle.com> <20150918135411.GA25593@nazgul.tnic> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: <20150918135411.GA25593@nazgul.tnic> Sender: kvm-owner@vger.kernel.org To: Borislav Petkov Cc: Konrad Rzeszutek Wilk , Cole Robinson , Xen Devel , Paolo Bonzini , kvm list , M A Young , xen List-Id: xen-devel@lists.xenproject.org On Fri, Sep 18, 2015 at 6:54 AM, Borislav Petkov wrote: > On Thu, Sep 17, 2015 at 01:23:31PM -0700, Andy Lutomirski wrote: >> Cc: Borislav. Is TSEG guaranteed to exist? Can we defer that until > > Why not? It is the tseg base address. > > I think this is kvm injecting a #GP as it is not ignoring this MSR. > Presumably modprobing kvm with "ignore_msrs=1" or so should hide the > issue IIUC... But the issue should be fixed, no? Does anyone know why this affects Xen on KVM but not native Linux on KVM? Or is there something weird about the particular KVM configuration? In any event, Borislav, you must have typed rdmsr_safe for a reason :) Either rdmsr_safe in that context is broken on Xen and not native (which is entirely possible -- I didn't check carefully) or the rdmsr_safe isn't "safe" on any type of kernel. Persumably either the kernel or KVM (or both) should be fixed. Given that we can handle fixups in the decompressor, surely it wouldn't be so hard to make early GPF fixups work in the main kernel. --Andy