On Fri, Feb 09, 2018 at 02:01:33PM +0100, Vitaly Kuznetsov wrote: > 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@xxxxxxxxxx> > --- > - Radim's suggestion was to disable DIRECTED_EOI unconditionally but I'm not > that radical :-) In theory, we may have multiple IOAPICs in userspace in > future and DIRECTED_EOI can be leveraged. I sort of agree on this, especially considering that we already have IOAPIC version 0x20 support in QEMU already. > --- > arch/x86/kvm/lapic.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 924ac8ce9d50..5339287fee63 100644 > --- 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); > } > -- > 2.14.3 > Does this mean that we can avoid the migration problem that Radim raised in previous discussion? Basically the OSs should only probe this version once for each boot, if so I think it should be fine. But since you didn't mention that in either commit message and comment, I would like to ask and confirm. For the change itself, it looks sane to me. Thanks, -- Peter Xu
