On Wed, 2022-08-31 at 00:35 +0000, Sean Christopherson wrote:
> Explicitly skip the optimized map setup if the vCPU's LDR is '0', i.e. if
> the vCPU will never response to logical mode interrupts. KVM already
> skips setup in this case, but relies on kvm_apic_map_get_logical_dest()
> to generate mask==0. KVM still needs the mask=0 check as a non-zero LDR
> can yield mask==0 depending on the mode, but explicitly handling the LDR
> will make it simpler to clean up the logical mode tracking in the future.
If I am not mistaken, the commit description is a bit misleading - in this case we just don't add
the vCPU to the map since it is unreachable, but we do continue creating the map.
Best regards,
MaxiM Levitsky
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/lapic.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index c224b5c7cd92..8209caffe3ab 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -318,10 +318,12 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
> continue;
>
> ldr = kvm_lapic_get_reg(apic, APIC_LDR);
> + if (!ldr)
> + continue;
>
> if (apic_x2apic_mode(apic)) {
> new->mode |= KVM_APIC_MODE_X2APIC;
> - } else if (ldr) {
> + } else {
> ldr = GET_APIC_LOGICAL_ID(ldr);
> if (kvm_lapic_get_reg(apic, APIC_DFR) == APIC_DFR_FLAT)
> new->mode |= KVM_APIC_MODE_XAPIC_FLAT;