linux-kernel - [PATCH v2] KVM: VMX: Enable MSR-BASED TPR shadow even if w/o APICv

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Date:   Tue, 20 Sep 2016 08:35:46 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Wanpeng Li <wanpeng.li@...mail.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wincy Van <fanwenyi0529@...il.com>,
        Yang Zhang <yang.zhang.wz@...il.com>
Subject: [PATCH v2] KVM: VMX: Enable MSR-BASED TPR shadow even if w/o APICv

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: 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>
---
v1 -> v2: 
 * leverage the cached msr bitmap

 arch/x86/kvm/vmx.c | 35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 5cede40..7d884e1 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6464,17 +6464,23 @@ 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_apicv) {
+		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 (cpu_has_vmx_tpr_shadow()) {
+		/* TPR */
+		vmx_disable_intercept_msr_read_x2apic(0x808);
+		vmx_disable_intercept_msr_write_x2apic(0x808);
+	}
 
 	if (enable_ept) {
 		kvm_mmu_set_mask_ptes(VMX_EPT_READABLE_MASK,
@@ -8435,12 +8441,7 @@ 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))
-- 
1.9.1