KVM: lapic: stop advertising DIRECTED_EOI when in-kernel IOAPIC is in use

Devices which use level-triggered interrupts under Windows 2016 with
Hyper-V role enabled don't work: Windows disables EOI broadcast in SPIV
unconditionally. Our in-kernel IOAPIC implementation emulates an old IOAPIC
version which has no EOI register so EOI never happens.

The issue was discovered and discussed a while ago:
https://www.spinics.net/lists/kvm/msg148098.html

While this is a guest OS bug (it should check that IOAPIC has the required
capabilities before disabling EOI broadcast) we can workaround it in KVM:
advertising DIRECTED_EOI with in-kernel IOAPIC makes little sense anyway.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 391dda8d43b7a44d3cedd0b41edbb51ba7171bf4..70dcb554802289910382762f44e7a20b07d3317a 100644 (file)
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -321,8 +321,16 @@ void kvm_apic_set_version(struct kvm_vcpu *vcpu)
        if (!lapic_in_kernel(vcpu))
                return;
 
+       /*
+        * KVM emulates 82093AA datasheet (with in-kernel IOAPIC implementation)
+        * which doesn't have EOI register; Some buggy OSes (e.g. Windows with
+        * Hyper-V role) disable EOI broadcast in lapic not checking for IOAPIC
+        * version first and level-triggered interrupts never get EOIed in
+        * IOAPIC.
+        */
        feat = kvm_find_cpuid_entry(apic->vcpu, 0x1, 0);
-       if (feat && (feat->ecx & (1 << (X86_FEATURE_X2APIC & 31))))
+       if (feat && (feat->ecx & (1 << (X86_FEATURE_X2APIC & 31))) &&
+           !ioapic_in_kernel(vcpu->kvm))
                v |= APIC_LVR_DIRECTED_EOI;
        kvm_lapic_set_reg(apic, APIC_LVR, v);
 }