Re: [PATCH v3 1/6] KVM: nVMX: Use hardware MSR bitmap

[Wincy Van]

On Wed, Jan 28, 2015 at 4:05 PM, Zhang, Yang Z <yang.z.zhang@xxxxxxxxx> wrote:
>> @@ -8344,7 +8394,68 @@ static int
>> nested_vmx_check_msr_bitmap_controls(struct kvm_vcpu *vcpu,  static
>> inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu,
>>                                                struct vmcs12
>> *vmcs12)  {
>> -       return false;
>> +       struct page *page;
>> +       unsigned long *msr_bitmap;
>> +
>> +       if (!nested_cpu_has_virt_x2apic_mode(vmcs12))
>> +               return false;
>> +
>> +       page = nested_get_page(vcpu, vmcs12->msr_bitmap);
>> +       if (!page) {
>> +               WARN_ON(1);
>> +               return false;
>> +       }
>> +       msr_bitmap = (unsigned long *)kmap(page);
>> +       if (!msr_bitmap) {
>> +               nested_release_page_clean(page);
>> +               WARN_ON(1);
>> +               return false;
>> +       }
>> +
>> +       memset(vmx_msr_bitmap_nested, 0xff, PAGE_SIZE);
>> +
>> +       if (nested_cpu_has_virt_x2apic_mode(vmcs12))
>> +               /* TPR is allowed */
>> +               nested_vmx_disable_intercept_for_msr(msr_bitmap,
>> +                               vmx_msr_bitmap_nested,
>> +                               APIC_BASE_MSR + (APIC_TASKPRI >>
>> 4),
>> +                               MSR_TYPE_R | MSR_TYPE_W);
>
> I didn't understand what this function does? Per my understanding, you only need to set the (vmx_msr_bitmap_nested = vmcs01->msr_bitmap | vmcs12->msr_bitmap) and inject the nested vmexit to L1 if the bit in vmcs12->msr_bitmap is setting. Am I missing some patches?

In the beginning, I want to do "vmcs01->msr_bitmap |
vmcs12->msr_bitmap", but I remember that there isn't a instruction to
do a bit or operation in two pages effectively, so I do the bit or
operation in nested_vmx_disable_intercept_for_msr. If the hardware do
not support this, I think it is faster if we deal with the bits on
demand. nested_vmx_merge_msr_bitmap is used to merge L0's and L1's
bitmaps, any features can put their logic here.

If there is a faster way, please teach me how to do it : )

Thanks,
Wincy


>
> Best regards,
> Yang
>
>
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