linux-kernel - Re: [PATCH 2/3] KVM: vmx: simplify MSR bitmap setup

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Date:   Wed, 20 Dec 2017 11:40:07 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH 2/3] KVM: vmx: simplify MSR bitmap setup

This doesn't look right to me. Without APIC-register virtualization,
the only X2APIC MSR intercept that should be disabled is TPR.

On Wed, Dec 20, 2017 at 4:05 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
> The APICv-enabled MSR bitmap is a superset of the APICv-disabled bitmap.
> Make that obvious in vmx_disable_intercept_msr_x2apic.
>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/vmx.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 9f9c3194440f..905aaa778306 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5263,12 +5263,9 @@ static void vmx_disable_intercept_msr_x2apic(u32 msr, int type, bool apicv_activ
>                                 msr, type);
>                 __vmx_disable_intercept_for_msr(vmx_msr_bitmap_longmode_x2apic_apicv,
>                                 msr, type);
> -       } else {
> -               __vmx_disable_intercept_for_msr(vmx_msr_bitmap_legacy_x2apic,
> -                               msr, type);
> -               __vmx_disable_intercept_for_msr(vmx_msr_bitmap_longmode_x2apic,
> -                               msr, type);
>         }
> +       __vmx_disable_intercept_for_msr(vmx_msr_bitmap_legacy_x2apic, msr, type);
> +       __vmx_disable_intercept_for_msr(vmx_msr_bitmap_longmode_x2apic, msr, type);
>  }
>
>  static bool vmx_get_enable_apicv(struct kvm_vcpu *vcpu)
> @@ -7148,7 +7145,6 @@ static __init int hardware_setup(void)
>          * TPR reads and writes can be virtualized even if virtual interrupt
>          * delivery is not in use.
>          */
> -       vmx_disable_intercept_msr_x2apic(0x808, MSR_TYPE_W, true);
>         vmx_disable_intercept_msr_x2apic(0x808, MSR_TYPE_R | MSR_TYPE_W, false);
>
>         /* EOI */
> --
> 1.8.3.1
>
>