linux-kernel - Re: [PATCH v3 24/25] KVM: TDX: Guard VM state transitions with "all" the locks

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Message-ID: <8f8b4041abb730ed7dec97aaa7a8273fe680d87a.camel@intel.com>
Date: Fri, 24 Oct 2025 10:53:33 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "chenhuacai@...nel.org" <chenhuacai@...nel.org>, "frankja@...ux.ibm.com"
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CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "linux-coco@...ts.linux.dev"
	<linux-coco@...ts.linux.dev>, "Zhao, Yan Y" <yan.y.zhao@...el.com>,
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 Rick P" <rick.p.edgecombe@...el.com>, "linux-mips@...r.kernel.org"
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Subject: Re: [PATCH v3 24/25] KVM: TDX: Guard VM state transitions with "all"
 the locks


>  
> +typedef void *tdx_vm_state_guard_t;
> +
> +static tdx_vm_state_guard_t tdx_acquire_vm_state_locks(struct kvm *kvm)
> +{
> +	int r;
> +
> +	mutex_lock(&kvm->lock);
> +
> +	if (kvm->created_vcpus != atomic_read(&kvm->online_vcpus)) {
> +		r = -EBUSY;
> +		goto out_err;
> +	}
> +
> +	r = kvm_lock_all_vcpus(kvm);
> +	if (r)
> +		goto out_err;
> +
> +	/*
> +	 * Note the unintuitive ordering!  vcpu->mutex must be taken outside
> +	 * kvm->slots_lock!
> +	 */
> +	mutex_lock(&kvm->slots_lock);
> +	return kvm;
> +
> +out_err:
> +	mutex_unlock(&kvm->lock);
> +	return ERR_PTR(r);
> +}
> +
> +static void tdx_release_vm_state_locks(struct kvm *kvm)
> +{
> +	mutex_unlock(&kvm->slots_lock);
> +	kvm_unlock_all_vcpus(kvm);
> +	mutex_unlock(&kvm->lock);
> +}
> +
> +DEFINE_CLASS(tdx_vm_state_guard, tdx_vm_state_guard_t,
> +	     if (!IS_ERR(_T)) tdx_release_vm_state_locks(_T),
> +	     tdx_acquire_vm_state_locks(kvm), struct kvm *kvm);
> +
>  static int tdx_td_init(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
>  {
>  	struct kvm_tdx_init_vm __user *user_data = u64_to_user_ptr(cmd->data);
> @@ -2644,6 +2684,10 @@ static int tdx_td_init(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
>  	BUILD_BUG_ON(sizeof(*init_vm) != 256 + sizeof_field(struct kvm_tdx_init_vm, cpuid));
>  	BUILD_BUG_ON(sizeof(struct td_params) != 1024);
>  
> +	CLASS(tdx_vm_state_guard, guard)(kvm);
> +	if (IS_ERR(guard))
> +		return PTR_ERR(guard);
> +
>  	if (kvm_tdx->state != TD_STATE_UNINITIALIZED)
>  		return -EINVAL;
>  
> @@ -2743,7 +2787,9 @@ static int tdx_td_finalize(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
>  {
>  	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
>  
> -	guard(mutex)(&kvm->slots_lock);
> +	CLASS(tdx_vm_state_guard, guard)(kvm);
> +	if (IS_ERR(guard))
> +		return PTR_ERR(guard);
>  

Since you are changing both tdx_td_init() and tdx_td_finalize(), maybe
just changing tdx_vm_ioctl() instead (like tdx_vcpu_unlocked_ioctl())?  
This is not required for tdx_get_capabilities() but there's no harm to do
it too AFACIT.