linux-kernel - Re: [PATCH v4] KVM: nVMX: nested TPR shadow/threshold emulation

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Date:	Wed, 20 Aug 2014 14:59:14 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Jan Kiszka <jan.kiszka@...mens.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...nel.org>, Bandan Das <bsd@...hat.com>,
	Zhang Yang <yang.z.zhang@...el.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] KVM: nVMX: nested TPR shadow/threshold emulation

Hi Paolo,
On Tue, Aug 19, 2014 at 10:34:20AM +0200, Paolo Bonzini wrote:
>Il 19/08/2014 10:30, Wanpeng Li ha scritto:
>> +		if (vmx->nested.virtual_apic_page)
>> +			nested_release_page(vmx->nested.virtual_apic_page);
>> +		vmx->nested.virtual_apic_page =
>> +		   nested_get_page(vcpu, vmcs12->virtual_apic_page_addr);
>> +		if (!vmx->nested.virtual_apic_page)
>> +			exec_control &=
>> +				~CPU_BASED_TPR_SHADOW;
>> +		else
>> +			vmcs_write64(VIRTUAL_APIC_PAGE_ADDR,
>> +				page_to_phys(vmx->nested.virtual_apic_page));
>> +
>> +		/*
>> +		 * If CR8 load exits are enabled, CR8 store exits are enabled,
>> +		 * and virtualize APIC access is disabled, the processor would
>> +		 * never notice. Doing it unconditionally is not correct, but
>> +		 * it is the simplest thing.
>> +		 */
>> +		if (!(exec_control & CPU_BASED_TPR_SHADOW) &&
>> +			!((exec_control & CPU_BASED_CR8_LOAD_EXITING) &&
>> +				(exec_control & CPU_BASED_CR8_STORE_EXITING)))
>> +			nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
>> +
>
>You aren't checking "virtualize APIC access" here, but the comment
>mentions it.
>
>As the comment says, failing the entry unconditionally could be the
>simplest thing, which means moving the nested_vmx_failValid call inside
>the "if (!vmx->nested.virtual_apic_page)".
>
>If you want to check all of CR8_LOAD/CR8_STORE/VIRTUALIZE_APIC_ACCESS,
>please mention in the comment that failing the vm entry is _not_ what
>the processor does but it's basically the only possibility we have.  In
>that case, I would also place the "if" within the "if
>(!vmx->nested.virtual_apic_page)": it also simplifies the condition
>because you don't have to check CPU_BASED_TPR_SHADOW anymore.
>
>You can send v5 with these changes, and I'll apply it for 3.18.  Thanks!
>

Do you mean this? 

+	/*
+	 * Failing the vm entry is _not_ what the processor does
+	 * but it's basically the only possibility we have.
+	 */
+	if (!vmx->nested.virtual_apic_page)
+		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);

Regards,
Wanpeng Li 

>Paolo
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