Re: rdmsr_safe in Linux PV (under Xen) gets an #GP:Re: [Fedora-xen] Running fedora xen on top of KVM?

[Andy Lutomirski <luto@amacapital.net>]

On Fri, Sep 18, 2015 at 6:54 AM, Borislav Petkov <bp@alien8.de> 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