linux-kernel - Re: [PATCH v12 07/22] x86/virt/tdx: Add skeleton to enable TDX on demand

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Date:   Wed, 28 Jun 2023 15:04:19 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kai Huang <kai.huang@...el.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, dave.hansen@...el.com,
        kirill.shutemov@...ux.intel.com, tony.luck@...el.com,
        tglx@...utronix.de, bp@...en8.de, mingo@...hat.com, hpa@...or.com,
        seanjc@...gle.com, pbonzini@...hat.com, david@...hat.com,
        dan.j.williams@...el.com, rafael.j.wysocki@...el.com,
        ashok.raj@...el.com, reinette.chatre@...el.com,
        len.brown@...el.com, ak@...ux.intel.com, isaku.yamahata@...el.com,
        ying.huang@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, nik.borisov@...e.com,
        bagasdotme@...il.com, sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v12 07/22] x86/virt/tdx: Add skeleton to enable TDX on
 demand

On Tue, Jun 27, 2023 at 02:12:37AM +1200, 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);
> +
> +	if (tdx_global_initialized) {
> +		ret = 0;
> +		goto out;
> +	}
> +
> +	/* All '0's are just unused parameters. */
> +	ret = seamcall(TDH_SYS_INIT, 0, 0, 0, 0, NULL, NULL);
> +	if (!ret)
> +		tdx_global_initialized = true;
> +out:
> +	raw_spin_unlock_irqrestore(&tdx_global_init_lock, flags);
> +
> +	return ret;
> +}

How long does that TDX_SYS_INIT take and why is a raw_spinlock with IRQs
disabled the right way to serialize this?