3.16.67-rc1 review patch. If anyone has any objections, please let me know.
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From: Joerg Roedel jroedel@suse.de
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 jroedel@suse.de Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/x86/kvm/vmx.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -4224,7 +4224,9 @@ static u8 vmx_msr_bitmap_mode(struct kvm { 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;