linux-kernel - Re: [RFC 7/7] KVM: VMX: Enable PKS for nested VM

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Date:   Wed, 12 Aug 2020 08:00:17 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Chenyi Qiang <chenyi.qiang@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 7/7] KVM: VMX: Enable PKS for nested VM

On Mon, Aug 10, 2020 at 05:05:36PM -0700, Jim Mattson wrote:
> On Fri, Aug 7, 2020 at 1:47 AM Chenyi Qiang <chenyi.qiang@...el.com> wrote:
> >
> > PKS MSR passes through guest directly. Configure the MSR to match the
> > L0/L1 settings so that nested VM runs PKS properly.
> >
> > Signed-off-by: Chenyi Qiang <chenyi.qiang@...el.com>
> > ---
> >  arch/x86/kvm/vmx/nested.c | 32 ++++++++++++++++++++++++++++++++
> >  arch/x86/kvm/vmx/vmcs12.c |  2 ++
> >  arch/x86/kvm/vmx/vmcs12.h |  6 +++++-
> >  arch/x86/kvm/vmx/vmx.c    | 10 ++++++++++
> >  arch/x86/kvm/vmx/vmx.h    |  1 +
> >  5 files changed, 50 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index df2c2e733549..1f9823d21ecd 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -647,6 +647,12 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
> >                                         MSR_IA32_PRED_CMD,
> >                                         MSR_TYPE_W);
> >
> > +       if (!msr_write_intercepted_l01(vcpu, MSR_IA32_PKRS))
> > +               nested_vmx_disable_intercept_for_msr(
> > +                                       msr_bitmap_l1, msr_bitmap_l0,
> > +                                       MSR_IA32_PKRS,
> > +                                       MSR_TYPE_R | MSR_TYPE_W);
> 
> What if L1 intercepts only *reads* of MSR_IA32_PKRS?

nested_vmx_disable_intercept_for_msr() handles merging L1's desires, the
(MSR_TYPE_R | MSR_TYPE_W) param is effectively L0's desire for L2.