Re: [PATCH 8/8] x86: KVM guest: VMX cr3 cache support

[Avi Kivity <avi@qumranet.com>]

Zhao Forrest wrote:
>> * We only need to hook operations that are MMU writes. We hook these so
>> that
>> * we can use lazy MMU mode to batch these operations. We could probably
>> * improve the performance of the host code if we used some of the
>> information
>> @@ -219,6 +359,9 @@ static void paravirt_ops_setup(void)
>> pv_mmu_ops.lazy_mode.enter = kvm_enter_lazy_mmu;
>> pv_mmu_ops.lazy_mode.leave = kvm_leave_lazy_mmu;
>> }
>> +
>> +	if (kvm_para_has_feature(KVM_FEATURE_CR3_CACHE))
>>     
> Here guest OS calls cpuid() to know if KVM_FEATURE_CR3_CACHE is
> supported by KVM, so I think that the kernel counterpart of this
> patch(i.e. [kvm-devel] [PATCH 7/8] KVM: MMU: VMX cr3 cache support)
> should include the code to intercept cpuid trap and set
> KVM_FEATURE_CR3_CACHE. But I didn't find such code in [PATCH 7/8] KVM:
> MMU: VMX cr3 cache support. Do I miss anything relevant?
>
>   

Userspace sets the cpuid information; this allows, for example, command 
line switches to hide paravirtualization support.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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