Commit 0bcc3fb9 authored Feb 09, 2018 by Vitaly Kuznetsov Committed by Paolo Bonzini Mar 16, 2018

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>

parent c51eb52b

arch/x86/kvm/lapic.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -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);
		}

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