2014-11-06 10:34+0100, Paolo Bonzini:
> On 05/11/2014 21:45, Nadav Amit wrote:
> > If I understand the SDM correctly, in such scenario (all APICs are
> > software disabled) the mode is left as the default - flat mode (see
APIC doesn't have any global mode (it is just KVM's simplification), so
when a message lands on the system bus, it just compares MDA with LDR
and DFR ...
> > section 10.6.2.2 "Logical Destination Mode”): "All processors that
> > have their APIC software enabled (using the spurious vector
> > enable/disable bit) must have their DFRs (Destination Format
> > Registers) programmed identically. The default mode for DFR is flat
> > mode.”
I think the "default mode" points to reset state, which is flat DFR;
and it is mentioned only because of the following sentence
If you are using cluster mode, DFRs must be programmed before the APIC
is software enabled.
> That's not what either Bochs or QEMU do, though. (Though in the case of
> Bochs I cannot find the place where reception of IPIs is prevented for
> software-disabled APICs, so I'm not sure how much to trust it in this case).
>
> I'm not sure why software-disabled APICs could have different DFRs, if
> the APICs can receive NMI IPIs. I'll ask Intel.
When changing the mode, we can't switch DFR synchronously, so it has to
happen and NMI may be needed (watchdog?) before APIC configuration.
Explicit statement might have been a hint to be _extra_ careful when
using logical destination for INIT, NMI, ... I wonder what they'll say.
Anyway, Paolo's patch seems to be in the right direction, I'd modify it
a bit though:
LDR=0 isn't addressable in any logical mode, so we can ignore APICs that
don't set it and decide the mode by the last nonzero one.
This works in a situation, where one part is configured for cluster and
the rest is still in reset state.
(It gets harder if we allow nonzero LDRs with different DFR ...
we'd need to split our logical map to handle it.)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 758f838..6da303e1 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -148,10 +148,6 @@ static void recalculate_apic_map(struct kvm *kvm)
goto out;
new->ldr_bits = 8;
- /* flat mode is default */
- new->cid_shift = 8;
- new->cid_mask = 0;
- new->lid_mask = 0xff;
new->broadcast = APIC_BROADCAST;
kvm_for_each_vcpu(i, vcpu, kvm) {
@@ -166,7 +162,7 @@ static void recalculate_apic_map(struct kvm *kvm)
new->cid_mask = (1 << KVM_X2APIC_CID_BITS) - 1;
new->lid_mask = 0xffff;
new->broadcast = X2APIC_BROADCAST;
- } else if (kvm_apic_hw_enabled(apic)) {
+ } else if (kvm_apic_get_reg(apic, APIC_LDR)) {
if (kvm_apic_get_reg(apic, APIC_DFR) ==
APIC_DFR_CLUSTER) {
new->cid_shift = 4;
--
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