Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1691200 > unrolled thread

Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-19 11:40 +0200
    Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-19 20:00 +0200

#1691200 — Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor

2017-07-17 13:58-0400, Bandan Das:
> Radim Krčmář <rkrcmar@redhat.com> writes:
> ...
>>> > and no other mentions of a VM exit, so I think that the VM exit happens
>>> > only under these conditions:
>>> >
>>> >   — The EPT memory type (bits 2:0) must be a value supported by the
>>> >     processor as indicated in the IA32_VMX_EPT_VPID_CAP MSR (see
>>> >     Appendix A.10).
>>> >   — Bits 5:3 (1 less than the EPT page-walk length) must be 3, indicating
>>> >     an EPT page-walk length of 4; see Section 28.2.2.
>>> >   — Bit 6 (enable bit for accessed and dirty flags for EPT) must be 0 if
>>> >     bit 21 of the IA32_VMX_EPT_VPID_CAP MSR (see Appendix A.10) is read
>>> >     as 0, indicating that the processor does not support accessed and
>>> >     dirty flags for EPT.
>>> >   — Reserved bits 11:7 and 63:N (where N is the processor’s
>>> >     physical-address width) must all be 0.
>>> >
>>> > And it looks like we need parts of nested_ept_init_mmu_context() to
>>> > properly handle VMX_EPT_AD_ENABLE_BIT.
>>> 
>>> I completely ignored AD and the #VE sections. I will add a TODO item
>>> in the comment section.
>>
>> AFAIK, we don't support #VE, but AD would be nice to handle from the
>> beginning.  (I think that caling nested_ept_init_mmu_context() as-is
>> isn't that bad.)
> 
> I went back to the spec to take a look at the AD handling. It doesn't look
> like anything needs to be done since nested_ept_init_mmu_context() is already
> being called with the correct eptp in prepare_vmcs02 ? Anything else that
> needs to be done for AD handling in vmfunc context ?

AD is decided by EPTP bit 6, so it can be toggled by EPTP switching and
we don't call prepare_vmcs02() after emulating VMFUNC vm exit.
We want to forward the new AD configuration to KVM's MMU.

[toc] | [next] | [standalone]

#1692075 — Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor

Radim Krčmář <rkrcmar@redhat.com> writes:

> 2017-07-17 13:58-0400, Bandan Das:
>> Radim Krčmář <rkrcmar@redhat.com> writes:
>> ...
>>>> > and no other mentions of a VM exit, so I think that the VM exit happens
>>>> > only under these conditions:
>>>> >
>>>> >   — The EPT memory type (bits 2:0) must be a value supported by the
>>>> >     processor as indicated in the IA32_VMX_EPT_VPID_CAP MSR (see
>>>> >     Appendix A.10).
>>>> >   — Bits 5:3 (1 less than the EPT page-walk length) must be 3, indicating
>>>> >     an EPT page-walk length of 4; see Section 28.2.2.
>>>> >   — Bit 6 (enable bit for accessed and dirty flags for EPT) must be 0 if
>>>> >     bit 21 of the IA32_VMX_EPT_VPID_CAP MSR (see Appendix A.10) is read
>>>> >     as 0, indicating that the processor does not support accessed and
>>>> >     dirty flags for EPT.
>>>> >   — Reserved bits 11:7 and 63:N (where N is the processor’s
>>>> >     physical-address width) must all be 0.
>>>> >
>>>> > And it looks like we need parts of nested_ept_init_mmu_context() to
>>>> > properly handle VMX_EPT_AD_ENABLE_BIT.
>>>> 
>>>> I completely ignored AD and the #VE sections. I will add a TODO item
>>>> in the comment section.
>>>
>>> AFAIK, we don't support #VE, but AD would be nice to handle from the
>>> beginning.  (I think that caling nested_ept_init_mmu_context() as-is
>>> isn't that bad.)
>> 
>> I went back to the spec to take a look at the AD handling. It doesn't look
>> like anything needs to be done since nested_ept_init_mmu_context() is already
>> being called with the correct eptp in prepare_vmcs02 ? Anything else that
>> needs to be done for AD handling in vmfunc context ?
>
> AD is decided by EPTP bit 6, so it can be toggled by EPTP switching and
> we don't call prepare_vmcs02() after emulating VMFUNC vm exit.
> We want to forward the new AD configuration to KVM's MMU.

Thanks, I had incorrectly assumed that prepare_vmcs02 will be called after
an exit unconditionally. I will work something up soon.

Bandan

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web