Re: [RFC PATCH v4 11/36] i386/tdx: Initialize TDX before creating TD vcpus

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On 5/23/2022 5:20 PM, Gerd Hoffmann wrote:
+int tdx_pre_create_vcpu(CPUState *cpu)
+{
+    MachineState *ms = MACHINE(qdev_get_machine());
+    X86CPU *x86cpu = X86_CPU(cpu);
+    CPUX86State *env = &x86cpu->env;
+    struct kvm_tdx_init_vm init_vm;
+    int r = 0;
+
+    qemu_mutex_lock(&tdx_guest->lock);
+    if (tdx_guest->initialized) {
+        goto out;
+    }
+
+    memset(&init_vm, 0, sizeof(init_vm));
+    init_vm.cpuid.nent = kvm_x86_arch_cpuid(env, init_vm.entries, 0);
+
+    init_vm.attributes = tdx_guest->attributes;
+    init_vm.max_vcpus = ms->smp.cpus;
+
+    r = tdx_vm_ioctl(KVM_TDX_INIT_VM, 0, &init_vm);
+    if (r < 0) {
+        error_report("KVM_TDX_INIT_VM failed %s", strerror(-r));
+        goto out;
+    }
+
+    tdx_guest->initialized = true;
+
+out:
+    qemu_mutex_unlock(&tdx_guest->lock);
+    return r;
+}

Hmm, hooking *vm* initialization into *vcpu* creation looks wrong to me.

That's because for TDX, it has to do VM-scope (feature) initialization before creating vcpu. This is new to KVM and QEMU, that every feature is vcpu-scope and configured per-vcpu before.

To minimize the change to QEMU, we want to utilize @cpu and @cpu->env to grab the configuration info. That's why it goes this way.

Do you have any better idea on it?

take care,
   Gerd





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