linux-kernel - Re: [PATCH v3] Enable MSR-BASED TPR shadow even if APICv is inactive

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Date:   Wed, 21 Sep 2016 18:35:07 +0200
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wincy Van <fanwenyi0529@...il.com>,
        Yang Zhang <yang.zhang.wz@...il.com>
Subject: Re: [PATCH v3] Enable MSR-BASED TPR shadow even if APICv is inactive

2016-09-21 10:14+0800, Wanpeng Li:
> 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.
> 
> Suggested-by: Radim Krčmář <rkrcmar@...hat.com>
> 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>
> ---
> v2 -> v3:
>  * introduce a new set of bitmaps and assign them in vmx_set_msr_bitmap()
> v1 -> v2: 
>  * leverage the cached msr bitmap
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> @@ -2518,10 +2520,18 @@ static void vmx_set_msr_bitmap(struct kvm_vcpu *vcpu)
>  	else if (cpu_has_secondary_exec_ctrls() &&
>  		 (vmcs_read32(SECONDARY_VM_EXEC_CONTROL) &
>  		  SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE)) {
> -		if (is_long_mode(vcpu))
> -			msr_bitmap = vmx_msr_bitmap_longmode_x2apic;
> -		else
> -			msr_bitmap = vmx_msr_bitmap_legacy_x2apic;
> +		if (enable_apicv && kvm_vcpu_apicv_active(vcpu)) {
> +			if (is_long_mode(vcpu))
> +				msr_bitmap = vmx_msr_bitmap_longmode_x2apic;
> +			else
> +				msr_bitmap = vmx_msr_bitmap_legacy_x2apic;
> +		} else if ((enable_apicv && !kvm_vcpu_apicv_active(vcpu)) ||
> +				!enable_apicv) {

Could only be "else" without if here.  I'll change that when refactoring
of vmx bitmap handling, posting soon (hopefully).

> +			if (is_long_mode(vcpu))
> +				msr_bitmap = vmx_msr_bitmap_longmode_x2apic_apicv_inactive;
> +			else
> +				msr_bitmap = vmx_msr_bitmap_legacy_x2apic_apicv_inactive;
> +		}
>  	} else {
>  		if (is_long_mode(vcpu))
>  			msr_bitmap = vmx_msr_bitmap_longmode;
> @@ -4678,28 +4688,49 @@ static void vmx_disable_intercept_for_msr(u32 msr, bool longmode_only)
> -static void vmx_enable_intercept_msr_read_x2apic(u32 msr)
> +static void vmx_enable_intercept_msr_read_x2apic(u32 msr, bool apicv_active)
>  {
> -	__vmx_enable_intercept_for_msr(vmx_msr_bitmap_legacy_x2apic,
> -			msr, MSR_TYPE_R);
> -	__vmx_enable_intercept_for_msr(vmx_msr_bitmap_longmode_x2apic,
> -			msr, MSR_TYPE_R);
> +	if (apicv_active) {
> +		__vmx_enable_intercept_for_msr(vmx_msr_bitmap_legacy_x2apic,
> +				msr, MSR_TYPE_R);
> +		__vmx_enable_intercept_for_msr(vmx_msr_bitmap_longmode_x2apic,
> +				msr, MSR_TYPE_R);
> +	} else {
> +		__vmx_disable_intercept_for_msr(vmx_msr_bitmap_legacy_x2apic_apicv_inactive,
> +				msr, MSR_TYPE_R);
> +		__vmx_disable_intercept_for_msr(vmx_msr_bitmap_longmode_x2apic_apicv_inactive,
> +				msr, MSR_TYPE_R);

Pasto here (disable vs. enable).  It's not called with !apicv_active and
the refactoring will delete the whole function, so

Reviwed-by: Radim Krčmář <rkrcmar@...hat.com>