From: Paolo Bonzini <pbonzini@redhat.com>
To: Jan Kiszka <jan.kiszka@siemens.com>,
Nadav Amit <nadav.amit@gmail.com>, kvm list <kvm@vger.kernel.org>
Subject: Re: Guest handling of IA32_DEBUGCTL MSR
Date: Tue, 28 Apr 2015 14:32:37 +0200 [thread overview]
Message-ID: <553F7DE5.1040100@redhat.com> (raw)
In-Reply-To: <553F765F.4050008@siemens.com>
On 28/04/2015 14:00, Jan Kiszka wrote:
> > > It seems strange that the guest is allowed to set IA32_DEBUGCTL MSR for the
> > > nested VM and get this value to the physical IA32_DEBUGCTL (see
> > > prepare_vmcs02), while it cannot set IA32_DEBUGCTL for itself (see
> > > kvm_set_msr_common).
> > >
> > > Am I missing something?
> >
> > No, it makes no sense.
>
> Are you sure that vmx is not allowing direct access to that MSR while in
> guest mode? We do save/restore it on all Intel CPUs, see
> setup_vmcs_config. Not sure about the AMD situation, though.
Right now, L1 could for example enable LBR for the L2 guest, but it
wouldn't make sense since the L1 guest cannot then read the last branch
MSRs.
Paolo
prev parent reply other threads:[~2015-04-28 12:32 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-28 11:42 Guest handling of IA32_DEBUGCTL MSR Nadav Amit
2015-04-28 11:43 ` Paolo Bonzini
2015-04-28 12:00 ` Jan Kiszka
2015-04-28 12:09 ` Nadav Amit
2015-04-28 12:32 ` Paolo Bonzini [this message]
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