From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] KVM: nVMX: nested TPR shadow/threshold emulation
Date: Thu, 31 Jul 2014 11:25:37 +0200
Message-ID: <53DA0B91.1010703@redhat.com>
References: <1406721880-5490-1-git-send-email-wanpeng.li@linux.intel.com> <53D90D5A.3060404@redhat.com> <20140731080353.GA3033@kernel>
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Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	Gleb Natapov <gleb@kernel.org>, Bandan Das <bsd@redhat.com>,
	Zhang Yang <yang.z.zhang@intel.com>, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org
To: Wanpeng Li <wanpeng.li@linux.intel.com>,
	Jan Kiszka <jan.kiszka@siemens.com>
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List-Id: kvm.vger.kernel.org

Il 31/07/2014 10:03, Wanpeng Li ha scritto:
>> One thing:
>>
>>> +	if (nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW))
>>> +		vmcs_write32(TPR_THRESHOLD, vmcs12->tpr_threshold);
>>
>> I think you can just do this write unconditionally, since most
>> hypervisors will enable this.  Also, you probably can add the tpr
> 
> What will happen if a hypervisor doesn't enable it? I make it more 
> cleaner in version two.

TPR_THRESHOLD will be likely written as zero, but the processor will
never use it anyway.  It's just a small optimization because
nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW) will almost always be true.

Paolo

>> threshold field to the read-write fields for shadow VMCS.
> 
> Agreed.
> 
> Regards,
> Wanpeng Li