Re: [PATCH 1/7] KVM: x86: Free vCPUs before freeing VM state

On Tue, Feb 25, 2025, Yan Zhao wrote:

quoted

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 58b82d6fd77c..045c61cc7e54 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c

@@ -12890,11 +12890,11 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 		mutex_unlock(&kvm->slots_lock);
 	}
 	kvm_unload_vcpu_mmus(kvm);
+	kvm_destroy_vcpus(kvm);
 	kvm_x86_call(vm_destroy)(kvm);
 	kvm_free_msr_filter(srcu_dereference_check(kvm->arch.msr_filter, &kvm->srcu, 1));
 	kvm_pic_destroy(kvm);
 	kvm_ioapic_destroy(kvm);
-	kvm_destroy_vcpus(kvm);
 	kvfree(rcu_dereference_check(kvm->arch.apic_map, 1));
 	kfree(srcu_dereference_check(kvm->arch.pmu_event_filter, &kvm->srcu, 1));
 	kvm_mmu_uninit_vm(kvm);

After this change, now the sequence is that

1. kvm_arch_pre_destroy_vm()
2. kvm_arch_destroy_vm()
   2.1 kvm_destroy_vcpus()
   2.2 .vm_destroy hook
   2.3 kvm_mmu_uninit_vm() --> mirror root ref is 1 upon here. Zap the mirror
                               root and reclaim SETP page table pages.
   2.4 .vm_free hook

Since TDX needs to reclaim the TDR page after reclaiming all other pages, we
currently added a vm_free hook at 2.4, after 2.3.

Could we move kvm_mmu_uninit_vm() before the .vm_destroy hook and after
kvm_destroy_vcpus()?

Or move the .vm_destroy hook after kvm_mmu_uninit_vm(), e.g. after
kvm_page_track_cleanup()?

I would go for the first option.  I'll tack on a patch since I need to test all
of these flows anyways, and I would much prefer to change course sooner rather
than later if it doesn't work for whatever reason.

Is this comment accurate?

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1e5f6f820c0b..f5685f153e08 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c

@@ -12874,13 +12874,19 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
                mutex_unlock(&kvm->slots_lock);
        }
        kvm_destroy_vcpus(kvm);
+
+       /*
+        * Do final MMU teardown prior to calling into vendor code.  All pages
+        * that were donated to the TDX module, e.g. for S-EPT tables, need to
+        * be reclaimed before the VM metadata page can be freed.
+        */
+       kvm_mmu_uninit_vm(kvm);
        kvm_x86_call(vm_destroy)(kvm);
        kvm_free_msr_filter(srcu_dereference_check(kvm->arch.msr_filter, &kvm->srcu, 1));
        kvm_pic_destroy(kvm);
        kvm_ioapic_destroy(kvm);
        kvfree(rcu_dereference_check(kvm->arch.apic_map, 1));
        kfree(srcu_dereference_check(kvm->arch.pmu_event_filter, &kvm->srcu, 1));
-       kvm_mmu_uninit_vm(kvm);
        kvm_page_track_cleanup(kvm);
        kvm_xen_destroy_vm(kvm);
        kvm_hv_destroy_vm(kvm);