From 1348f9af79db25e4e0c6475c5511e11969e82abc Mon Sep 17 00:00:00 2001 From: Joerg Roedel Date: Thu, 21 Feb 2019 15:30:48 +0000 Subject: [PATCH] KVM: VMX: Fix x2apic check in vmx_msr_bitmap_mode() The stable backport of upstream commit 904e14fb7cb96 KVM: VMX: make MSR bitmaps per-VCPU has a bug in vmx_msr_bitmap_mode(). It enables the x2apic MSR-bitmap when the kernel emulates x2apic for the guest in software. The upstream version of the commit checkes whether the hardware has virtualization enabled for x2apic emulation. Since KVM emulates x2apic for guests even when the host does not support x2apic in hardware, this causes the intercept of at least the X2APIC_TASKPRI MSR to be disabled on machines not supporting that MSR. The result is undefined behavior, on some machines (Intel Westmere based) it causes a crash of the guest kernel when it tries to access that MSR. Change the check in vmx_msr_bitmap_mode() to match the upstream code. This fixes the guest crashes observed with stable kernels starting with v4.4.168 through v4.4.175. Signed-off-by: Joerg Roedel Signed-off-by: Ben Hutchings --- arch/x86/kvm/vmx.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index bc3dc38fa4863..bd6b883f3075a 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -4224,7 +4224,9 @@ static u8 vmx_msr_bitmap_mode(struct kvm_vcpu *vcpu) { u8 mode = 0; - if (irqchip_in_kernel(vcpu->kvm) && apic_x2apic_mode(vcpu->arch.apic)) { + if (cpu_has_secondary_exec_ctrls() && + (vmcs_read32(SECONDARY_VM_EXEC_CONTROL) & + SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE)) { mode |= MSR_BITMAP_MODE_X2APIC; if (enable_apicv) mode |= MSR_BITMAP_MODE_X2APIC_APICV;