Defer updating SVI (i.e. the VMCS's highest ISR cache) when L2 is active,
but L1 has not enabled virtual interrupt delivery for L2, as an EOI that
is emulated _by KVM_ in such a case acts on L1's ISR, i.e. vmcs01 needs to
reflect the updated ISR when L1 is next run.

Note, L1's ISR is also effectively L2's ISR in such a setup, but because
virtual interrupt deliver is disable for L2, there's no need to update
SVI in vmcs02, because it will never be used.

v2:
 - WARN only if the vCPU is running to avoid false positives due to userspace
   stuffing APIC state while L2 is active. [Chao]
 - Grab Chao's Tested-by.

v1: https://lore.kernel.org/all/20241101192114.1810198-1-seanjc@google.com
Chao Gao (1):
  KVM: nVMX: Defer SVI update to vmcs01 on EOI when L2 is active w/o VID

Sean Christopherson (1):
  KVM: x86: Plumb in the vCPU to kvm_x86_ops.hwapic_isr_update()

 arch/x86/include/asm/kvm_host.h |  2 +-
 arch/x86/kvm/lapic.c            | 22 ++++++++++++++++------
 arch/x86/kvm/lapic.h            |  1 +
 arch/x86/kvm/vmx/nested.c       |  5 +++++
 arch/x86/kvm/vmx/vmx.c          | 23 ++++++++++++++++++++++-
 arch/x86/kvm/vmx/vmx.h          |  1 +
 arch/x86/kvm/vmx/x86_ops.h      |  2 +-
 7 files changed, 47 insertions(+), 9 deletions(-)


base-commit: 4d911c7abee56771b0219a9fbf0120d06bdc9c14
-- 
2.47.0.338.g60cca15819-goog

On Wed, 27 Nov 2024 16:00:08 -0800, Sean Christopherson wrote:
> Defer updating SVI (i.e. the VMCS's highest ISR cache) when L2 is active,
> but L1 has not enabled virtual interrupt delivery for L2, as an EOI that
> is emulated _by KVM_ in such a case acts on L1's ISR, i.e. vmcs01 needs to
> reflect the updated ISR when L1 is next run.
> 
> Note, L1's ISR is also effectively L2's ISR in such a setup, but because
> virtual interrupt deliver is disable for L2, there's no need to update
> SVI in vmcs02, because it will never be used.
> 
> [...]

Applied to kvm-x86 vmx, thanks!

[1/2] KVM: x86: Plumb in the vCPU to kvm_x86_ops.hwapic_isr_update()
      https://github.com/kvm-x86/linux/commit/76bce9f10162
[2/2] KVM: nVMX: Defer SVI update to vmcs01 on EOI when L2 is active w/o VID
      https://github.com/kvm-x86/linux/commit/b682d2fbf17c

--
https://github.com/kvm-x86/linux/tree/next