Re: [PATCH 2/2] KVM: nVMX: postpone VMCS changes on MSR_IA32_APICBASE write

From	Wanpeng Li <kernellwp@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/2] KVM: nVMX: postpone VMCS changes on MSR_IA32_APICBASE write
Date	2016-08-12 12:20 +0200
Message-ID	<s5hJg-lu-5@gated-at.bofh.it> (permalink)
References	<s3Xjz-4So-7@gated-at.bofh.it> <s3Xjz-4So-5@gated-at.bofh.it> <s5dPj-6mv-15@gated-at.bofh.it> <s5hge-8nx-15@gated-at.bofh.it>
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2016-08-12 17:44 GMT+08:00 Radim Krčmář <rkrcmar@redhat.com>:
> 2016-08-12 14:07+0800, Wanpeng Li:
>> 2016-08-09 2:16 GMT+08:00 Radim Krčmář <rkrcmar@redhat.com>:
>>> If vmcs12 does not intercept APIC_BASE writes, then KVM will handle the
>>> write with vmcs02 as the current VMCS.
>>> This will incorrectly apply modifications intended for vmcs01 to vmcs02
>>> and L2 can use it to gain access to L0's x2APIC registers by disabling
>>> virtualized x2APIC while using msr bitmap that assumes enabled.
>>>
>>> Postpone execution of vmx_set_virtual_x2apic_mode until vmcs01 is the
>>> current VMCS.  An alternative solution would temporarily make vmcs01 the
>>> current VMCS, but it requires more care.
>>
>> There is a scenario both L1 and L2 are running on x2apic mode, L1
>> don't own the APIC_BASE writes, then L2 is intended to disable x2apic
>> mode, however, your logic will also disable x2apic mode for L1.
>
> You mean a case where L1 does intercept APIC_BASE?
>
> That case is not affected, because it should cause a nested VM exit, so
> vmx_set_virtual_x2apic_mode() won't be called in the first place.

I mean L1 doesn't intercept APIC_BASE.

Regards,
Wanpeng Li

Thread

Re: [PATCH 2/2] KVM: nVMX: postpone VMCS changes on MSR_IA32_APICBASE write Wanpeng Li <kernellwp@gmail.com> - 2016-08-12 08:10 +0200
  Re: [PATCH 2/2] KVM: nVMX: postpone VMCS changes on  MSR_IA32_APICBASE write Radim Krčmář <rkrcmar@redhat.com> - 2016-08-12 11:50 +0200
    Re: [PATCH 2/2] KVM: nVMX: postpone VMCS changes on MSR_IA32_APICBASE write Wanpeng Li <kernellwp@gmail.com> - 2016-08-12 12:20 +0200
      Re: [PATCH 2/2] KVM: nVMX: postpone VMCS changes on  MSR_IA32_APICBASE write Radim Krčmář <rkrcmar@redhat.com> - 2016-08-12 13:40 +0200
        Re: [PATCH 2/2] KVM: nVMX: postpone VMCS changes on MSR_IA32_APICBASE write Wanpeng Li <kernellwp@gmail.com> - 2016-08-15 07:20 +0200
          Re: [PATCH 2/2] KVM: nVMX: postpone VMCS changes on  MSR_IA32_APICBASE write Radim Krčmář <rkrcmar@redhat.com> - 2016-08-15 16:40 +0200

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