linux-kernel - Re: [PATCH v11 07/20] x86/virt/tdx: Add skeleton to enable TDX on demand

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Message-ID: <e7c21694-d31b-4dbe-f75b-5a7c0127f5c8@intel.com>
Date:   Wed, 7 Jun 2023 08:22:36 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     linux-mm@...ck.org, kirill.shutemov@...ux.intel.com,
        tony.luck@...el.com, peterz@...radead.org, tglx@...utronix.de,
        seanjc@...gle.com, pbonzini@...hat.com, david@...hat.com,
        dan.j.williams@...el.com, rafael.j.wysocki@...el.com,
        ying.huang@...el.com, reinette.chatre@...el.com,
        len.brown@...el.com, ak@...ux.intel.com, isaku.yamahata@...el.com,
        chao.gao@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
        bagasdotme@...il.com, sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v11 07/20] x86/virt/tdx: Add skeleton to enable TDX on
 demand

On 6/4/23 07:27, Kai Huang wrote:
...
> +static int try_init_module_global(void)
> +{
> +	unsigned long flags;
> +	int ret;
> +
> +	/*
> +	 * The TDX module global initialization only needs to be done
> +	 * once on any cpu.
> +	 */
> +	raw_spin_lock_irqsave(&tdx_global_init_lock, flags);

Why is this "raw_"?

There's zero mention of it anywhere.

> +	if (tdx_global_init_status & TDX_GLOBAL_INIT_DONE) {
> +		ret = tdx_global_init_status & TDX_GLOBAL_INIT_FAILED ?
> +			-EINVAL : 0;
> +		goto out;
> +	}
> +
> +	/* All '0's are just unused parameters. */
> +	ret = seamcall(TDH_SYS_INIT, 0, 0, 0, 0, NULL, NULL);
> +
> +	tdx_global_init_status = TDX_GLOBAL_INIT_DONE;
> +	if (ret)
> +		tdx_global_init_status |= TDX_GLOBAL_INIT_FAILED;
> +out:
> +	raw_spin_unlock_irqrestore(&tdx_global_init_lock, flags);
> +
> +	return ret;
> +}
> +
> +/**
> + * tdx_cpu_enable - Enable TDX on local cpu
> + *
> + * Do one-time TDX module per-cpu initialization SEAMCALL (and TDX module
> + * global initialization SEAMCALL if not done) on local cpu to make this
> + * cpu be ready to run any other SEAMCALLs.
> + *
> + * Note this function must be called when preemption is not possible
> + * (i.e. via SMP call or in per-cpu thread).  It is not IRQ safe either
> + * (i.e. cannot be called in per-cpu thread and via SMP call from remote
> + * cpu simultaneously).

lockdep_assert_*() are your friends.  Unlike comments, they will
actually tell you if this goes wrong.

> +int tdx_cpu_enable(void)
> +{
> +	unsigned int lp_status;
> +	int ret;
> +
> +	if (!platform_tdx_enabled())
> +		return -EINVAL;
> +
> +	lp_status = __this_cpu_read(tdx_lp_init_status);
> +
> +	/* Already done */
> +	if (lp_status & TDX_LP_INIT_DONE)
> +		return lp_status & TDX_LP_INIT_FAILED ? -EINVAL : 0;
> +
> +	/*
> +	 * The TDX module global initialization is the very first step
> +	 * to enable TDX.  Need to do it first (if hasn't been done)
> +	 * before doing the per-cpu initialization.
> +	 */
> +	ret = try_init_module_global();
> +
> +	/*
> +	 * If the module global initialization failed, there's no point
> +	 * to do the per-cpu initialization.  Just mark it as done but
> +	 * failed.
> +	 */
> +	if (ret)
> +		goto update_status;
> +
> +	/* All '0's are just unused parameters */
> +	ret = seamcall(TDH_SYS_LP_INIT, 0, 0, 0, 0, NULL, NULL);
> +
> +update_status:
> +	lp_status = TDX_LP_INIT_DONE;
> +	if (ret)
> +		lp_status |= TDX_LP_INIT_FAILED;
> +
> +	this_cpu_write(tdx_lp_init_status, lp_status);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(tdx_cpu_enable);

You danced around it in the changelog, but the reason for the exports is
not clear.

> +static int init_tdx_module(void)
> +{
> +	/*
> +	 * TODO:
> +	 *
> +	 *  - Get TDX module information and TDX-capable memory regions.
> +	 *  - Build the list of TDX-usable memory regions.
> +	 *  - Construct a list of "TD Memory Regions" (TDMRs) to cover
> +	 *    all TDX-usable memory regions.
> +	 *  - Configure the TDMRs and the global KeyID to the TDX module.
> +	 *  - Configure the global KeyID on all packages.
> +	 *  - Initialize all TDMRs.
> +	 *
> +	 *  Return error before all steps are done.
> +	 */
> +	return -EINVAL;
> +}
> +
> +static int __tdx_enable(void)
> +{
> +	int ret;
> +
> +	ret = init_tdx_module();
> +	if (ret) {
> +		pr_err("TDX module initialization failed (%d)\n", ret);

Have you actually gone any  looked at how this pr_*()'s look?

Won't they say:

	tdx: TDX module initialized

Isn't that a _bit_ silly?  Why not just say:

	pr_info("module initialized.\n");