From: Roman Kagan <rkagan@virtuozzo.com>
Subject: [PATCH v3] kvm:vmx: more complete state update on APICv on/off
Date: 2016-05-18 14:48:20 GMT (1 day, 21 hours and 23 minutes ago)

The function to update APICv on/off state (in particular, to deactivate
it when enabling Hyper-V SynIC), used to be incomplete: it didn't adjust
APICv-related fields among secondary processor-based VM-execution
controls.

As a result, Windows 2012 guests would get stuck when SynIC-based
auto-EOI interrupt intersected with e.g. an IPI in the guest.

In addition, the MSR intercept bitmap wasn't updated to correspond to
whether "virtualize x2APIC mode" was enabled.  This path used not to be
triggered, since Windows didn't use x2APIC but rather their own
synthetic APIC access MSRs; however it represented a security risk
because the guest running in a SynIC-enabled VM could switch to x2APIC
and thus obtain direct access to host APIC MSRs (thanks to Yang Zhang
<yang.zhang.wz@gmail.com> for spotting this).

The patch fixes those omissions.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Cc: Steve Rutherford <srutherford@google.com>
Cc: Yang Zhang <yang.zhang.wz@gmail.com>
---
v2 -> v3:
 - only switch to x2apic msr bitmap if virtualize x2apic mode is on in vmcs

v1 -> v2:
 - only update relevant bits in the secondary exec control
 - update msr intercept bitmap (also make x2apic msr bitmap always
   correspond to APICv)

 arch/x86/kvm/vmx.c | 48 ++++++++++++++++++++++++++++++------------------
 1 file changed, 30 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index ee1c8a9..cef741a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2418,7 +2418,9 @@ static void vmx_set_msr_bitmap(struct kvm_vcpu *vcpu)

 	if (is_guest_mode(vcpu))
 		msr_bitmap = vmx_msr_bitmap_nested;
-	else if (vcpu->arch.apic_base & X2APIC_ENABLE) {
+	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
@@ -4783,6 +4785,19 @@ static void vmx_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
 	struct vcpu_vmx *vmx = to_vmx(vcpu);

 	vmcs_write32(PIN_BASED_VM_EXEC_CONTROL, vmx_pin_based_exec_ctrl(vmx));
+	if (cpu_has_secondary_exec_ctrls()) {
+		if (kvm_vcpu_apicv_active(vcpu))
+			vmcs_set_bits(SECONDARY_VM_EXEC_CONTROL,
+				      SECONDARY_EXEC_APIC_REGISTER_VIRT |
+				      SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY);
+		else
+			vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL,
+					SECONDARY_EXEC_APIC_REGISTER_VIRT |
+					SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY);
+	}
+
+	if (cpu_has_vmx_msr_bitmap())
+		vmx_set_msr_bitmap(vcpu);
 }

 static u32 vmx_exec_control(struct vcpu_vmx *vmx)
@@ -6329,23 +6344,20 @@ static __init int hardware_setup(void)

 	set_bit(0, vmx_vpid_bitmap); /* 0 is reserved for host */

-	if (enable_apicv) {
-		for (msr = 0x800; msr <= 0x8ff; msr++)
-			vmx_disable_intercept_msr_read_x2apic(msr);
-
-		/* According SDM, in x2apic mode, the whole id reg is used.
-		 * But in KVM, it only use the highest eight bits. Need to
-		 * intercept it */
-		vmx_enable_intercept_msr_read_x2apic(0x802);
-		/* 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);
-	}
+	for (msr = 0x800; msr <= 0x8ff; msr++)
+		vmx_disable_intercept_msr_read_x2apic(msr);
+
+	/* According SDM, in x2apic mode, the whole id reg is used.  But in
+	 * KVM, it only use the highest eight bits. Need to intercept it */
+	vmx_enable_intercept_msr_read_x2apic(0x802);
+	/* 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(0ull,
-- 
2.5.5