On Thu, Feb 27, 2014 at 07:05:49PM +0200, Michael S. Tsirkin wrote:
> apic polarity in KVM does not work: too many things assume active high.
> Let's not pretend it works, let's just ignore polarity flag. If we ever
> want to emulate it exactly, this will need a feature flag anyway.
>
> Also report this to userspace: this makes it
> possible to report the interrupt active-low
> in ACPI, this way we are closer to real hardware.
>
> This patch fixes OSX running on KVM.
>
> Reported-by: "Gabriel L. Somlo" <gso...@gmail.com>
> Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
>
> ---
>
> Gabriel, could you confirm this fixes OSX for you?
> If you can play with linux tweaking interrupt
> to active low, that would be very nice too:
> it's weekend here.
With Fedora 20 Live x86_64:
If all I do is 's/ActiveHigh/ActiveLow/' in hw/i386/[q36-]acpi-dsdt.dsl,
but otherwise don't try to change how QEMU deals with "logical" vs.
"physical" ioapic polarity, things work great. Printk's show polarity
set to 1, but with the ignore-polarity patch things work fine.
With normal (ActiveHigh) ACPI, printk reports polarity set to 0, and
things *still* work exactly the same.
So, the way I understand this (and I'm writing this mainly for myself,
to make sure I understand correctly, so please kick me if I got it
wrong), ACPI tells the guest OS how to configure "physical" ioapic polarity.
With ActiveHigh, "physical" == "logical", i.e. "high" == "asserted"
and "low" == "deasserted".
With ActiveLow, "physical" == !"logical", so the other way around.
QEMU being hard-coded to ActiveHigh is the moral equivalent of always
sending the kernel (KVM) "logical" line states, rather than "physical"
ones.
Assuming KVM's userland clients are all coded for ActiveHigh, we can
(should, for sanity's sake) just assume line states from userland are
logical, and stop paying attention the polarity bits. That way,
misbehaving guests [*] can configure their ioapics as they please, and
things will just work OK regardless.
As you pointed out earlier, even KVM itself already kind-of assumes
ActiveHigh (e.g. in __kvm_irq_line_state(), which should be coded
differently if ActiveLow were a serious possibility, and, BTW,
irq_states[irq] would probably have to be initialized to all-1's if
ActiveLow wre used, etc, etc).
[*] All Apple hardware is ActiveLow, and OS X has this as a hardcoded
assumption (it ignores ACPI's hints to the contrary). So OS X is one
of the misbehaving clients I mention above...
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 902f124..db29b27 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -674,6 +676,7 @@ struct kvm_ppc_smmu_info {
> #define KVM_CAP_ARM_EL1_32BIT 93
> #define KVM_CAP_SPAPR_MULTITCE 94
> #define KVM_CAP_EXT_EMUL_CPUID 95
> +#define KVM_CAP_X86_IOAPIC_POLARITY_IGNORED 96
For one thing, on current kvm git, this conflicts with
#define KVM_CAP_HYPERV_TIME 96
but the rest of the patch works (I've already been using it for quite
a while to get OS X guests to work...
Thanks much,
--Gabriel
>
> #ifdef KVM_CAP_IRQ_ROUTING
>
> diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
> index 2d68297..ad170b4 100644
> --- a/virt/kvm/ioapic.c
> +++ b/virt/kvm/ioapic.c
> @@ -328,7 +328,6 @@ int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int
> irq, int irq_source_id,
> irq_level = __kvm_irq_line_state(&ioapic->irq_states[irq],
> irq_source_id, level);
> entry = ioapic->redirtbl[irq];
> - irq_level ^= entry.fields.polarity;
> if (!irq_level) {
> ioapic->irr &= ~mask;
> ret = 1;
> --
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