linux-kernel - Re: [PATCH] KVM: VMX: Enable MSR-BASED TPR shadow even if w/o APICv

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Date:   Thu, 15 Sep 2016 08:30:52 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Mika Penttilä <mika.penttila@...tfour.com>,
        Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Wanpeng Li <wanpeng.li@...mail.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wincy Van <fanwenyi0529@...il.com>,
        Yang Zhang <yang.zhang.wz@...il.com>
Subject: Re: [PATCH] KVM: VMX: Enable MSR-BASED TPR shadow even if w/o APICv



On 15/09/2016 06:08, Mika Penttilä wrote:
> On 09/14/2016 10:58 AM, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> I observed that kvmvapic(to optimize flexpriority=N or AMD) is used 
>> to boost TPR access when testing kvm-unit-test/eventinj.flat tpr case
>> on my haswell desktop (w/ flexpriority, w/o APICv). Commit (8d14695f9542 
>> x86, apicv: add virtual x2apic support) disable virtual x2apic mode 
>> completely if w/o APICv, and the author also told me that windows guest
>> can't enter into x2apic mode when he developed the APICv feature several 
>> years ago. However, it is not truth currently, Interrupt Remapping and 
>> vIOMMU is added to qemu and the developers from Intel test windows 8 can 
>> work in x2apic mode w/ Interrupt Remapping enabled recently. 
>>
>> This patch enables TPR shadow for virtual x2apic mode to boost 
>> windows guest in x2apic mode even if w/o APICv.
>>
>> Can pass the kvm-unit-test.
>>
> 
> While at it, is the vmx flexpriotity stuff still valid code?
> AFAICS it gets enabled iff TPR shadow is on.

flexpriority is an Intel commercial name for TPR shadow.

Paolo

 flexpriority
> is on when :
> 
> (flexpriority_enabled && lapic_in_kernel && cpu_has_vmx_tpr_shadow && cpu_has_vmx_virtualize_apic_accesses)
> 
> But apic accesses to TPR mmio are not then trapped and TPR changes not reported because
> the “use TPR shadow” VM-execution control is 1.
> 
> Thanks,
> Mika
> 
> 
>> Suggested-by: Wincy Van <fanwenyi0529@...il.com>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: Wincy Van <fanwenyi0529@...il.com>
>> Cc: Yang Zhang <yang.zhang.wz@...il.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>>  arch/x86/kvm/vmx.c | 41 ++++++++++++++++++++++-------------------
>>  1 file changed, 22 insertions(+), 19 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 5cede40..e703129 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -6336,7 +6336,7 @@ static void wakeup_handler(void)
>>  
>>  static __init int hardware_setup(void)
>>  {
>> -	int r = -ENOMEM, i, msr;
>> +	int r = -ENOMEM, i;
>>  
>>  	rdmsrl_safe(MSR_EFER, &host_efer);
>>  
>> @@ -6464,18 +6464,6 @@ static __init int hardware_setup(void)
>>  
>>  	set_bit(0, vmx_vpid_bitmap); /* 0 is reserved for host */
>>  
>> -	for (msr = 0x800; msr <= 0x8ff; msr++)
>> -		vmx_disable_intercept_msr_read_x2apic(msr);
>> -
>> -	/* TMCCT */
>> -	vmx_enable_intercept_msr_read_x2apic(0x839);
>> -	/* TPR */
>> -	vmx_disable_intercept_msr_write_x2apic(0x808);
>> -	/* EOI */
>> -	vmx_disable_intercept_msr_write_x2apic(0x80b);
>> -	/* SELF-IPI */
>> -	vmx_disable_intercept_msr_write_x2apic(0x83f);
>> -
>>  	if (enable_ept) {
>>  		kvm_mmu_set_mask_ptes(VMX_EPT_READABLE_MASK,
>>  			(enable_ept_ad_bits) ? VMX_EPT_ACCESS_BIT : 0ull,
>> @@ -8435,12 +8423,7 @@ static void vmx_set_virtual_x2apic_mode(struct kvm_vcpu *vcpu, bool set)
>>  		return;
>>  	}
>>  
>> -	/*
>> -	 * There is not point to enable virtualize x2apic without enable
>> -	 * apicv
>> -	 */
>> -	if (!cpu_has_vmx_virtualize_x2apic_mode() ||
>> -				!kvm_vcpu_apicv_active(vcpu))
>> +	if (!cpu_has_vmx_virtualize_x2apic_mode())
>>  		return;
>>  
>>  	if (!cpu_need_tpr_shadow(vcpu))
>> @@ -8449,8 +8432,28 @@ static void vmx_set_virtual_x2apic_mode(struct kvm_vcpu *vcpu, bool set)
>>  	sec_exec_control = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
>>  
>>  	if (set) {
>> +		int msr;
>> +
>>  		sec_exec_control &= ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
>>  		sec_exec_control |= SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE;
>> +
>> +		if (kvm_vcpu_apicv_active(vcpu)) {
>> +			for (msr = 0x800; msr <= 0x8ff; msr++)
>> +				vmx_disable_intercept_msr_read_x2apic(msr);
>> +
>> +			/* TMCCT */
>> +			vmx_enable_intercept_msr_read_x2apic(0x839);
>> +			/* TPR */
>> +			vmx_disable_intercept_msr_write_x2apic(0x808);
>> +			/* EOI */
>> +			vmx_disable_intercept_msr_write_x2apic(0x80b);
>> +			/* SELF-IPI */
>> +			vmx_disable_intercept_msr_write_x2apic(0x83f);
>> +		} else if (vmx_exec_control(to_vmx(vcpu)) & CPU_BASED_TPR_SHADOW) {
>> +			/* TPR */
>> +			vmx_disable_intercept_msr_read_x2apic(0x808);
>> +			vmx_disable_intercept_msr_write_x2apic(0x808);
>> +		}
>>  	} else {
>>  		sec_exec_control &= ~SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE;
>>  		sec_exec_control |= SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
>>
> 
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