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

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Date:   Wed, 20 Dec 2017 22:13:46 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.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

On 20/12/2017 20:40, Jim Mattson wrote:
> This doesn't look right to me. Without APIC-register virtualization,
> the only X2APIC MSR intercept that should be disabled is TPR.

Of course...  The bitmap that has to be outside the "if" is
*_x2apic_apicv, not *_x2apic.  I sent the wrong version of the series
(and this was the only difference, together s/superset/subset/ in the
commit message).  Will resend tomorrow.

Paolo

> 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
>>
>>