KVM: nSVM: Ensure AVIC is inhibited when restoring a vCPU to guest mode

On nested VMRUN, KVM ensures AVIC is inhibited by requesting KVM_REQ_APICV_UPDATE, triggering a check of inhibit reasons, finding APICV_INHIBIT_REASON_NESTED, and disabling AVIC.

However, when KVM_SET_NESTED_STATE is performed on a vCPU not in guest mode with AVIC enabled, KVM_REQ_APICV_UPDATE is not requested, and AVIC is not inhibited.

Request KVM_REQ_APICV_UPDATE in the KVM_SET_NESTED_STATE path if AVIC is active, similar to the nested VMRUN path.

---

After the dust settles from all the inflight changes touching this area, we really need to reuse enter_svm_guest_mode() in svm_set_nested_state() imo. There are a few differences that will need to be addressed:

1. nested_vmcb02_prepare_save() needs to be skipped.

2. nested_svm_copy_common_state() may need to be skipped (or honestly, just folded into nested_vmcb02_prepare_save()?).

2. The CR3 value passed to nested_svm_load_cr3() needs to change.

3. Need to check if calling nested_svm_hv_update_vm_vp_ids() is okay/needed (might be another bug actually).

I think mostly likely we'll pass a boolean arg to enter_svm_guest_mode(), something like use_cached_save, and key 1 to 3 off of it. I don't like it (smells like from_vmrun), but it's the simplest way to avoid bugs like this in the future.

---
 arch/x86/kvm/svm/nested.c | 3 +++
 1 file changed, 3 insertions(+)

index de90b104a0dd5..82e512631e514 100644
@@ -1922,6 +1922,9 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 
 	svm->nested.force_msr_bitmap_recalc = true;
 
+	if (kvm_vcpu_apicv_active(vcpu))
+		kvm_make_request(KVM_REQ_APICV_UPDATE, vcpu);
+
 	kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
 	ret = 0;
 out_free:

2.53.0.414.gf7e9f6c205-goog

Applied to kvm-x86 nested, thanks!

[1/1] KVM: nSVM: Ensure AVIC is inhibited when restoring a vCPU to guest mode

      https://github.com/kvm-x86/linux/commit/24f7d36b824b

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