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

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Message-ID: <20230630092503.GC2533791@hirez.programming.kicks-ass.net>
Date:   Fri, 30 Jun 2023 11:25:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
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        "tglx@...utronix.de" <tglx@...utronix.de>,
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        "Chatre, Reinette" <reinette.chatre@...el.com>,
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        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
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        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v12 07/22] x86/virt/tdx: Add skeleton to enable TDX on
 demand

On Thu, Jun 29, 2023 at 12:00:44AM +0000, Huang, Kai wrote:

> The spec says it doesn't have a latency requirement, so theoretically it could
> be long.  SEAMCALL is a VMEXIT so it would at least cost thousands of cycles.

:-(

> If raw_spinlock isn't desired, I think I can introduce another function to do
> this and let the caller to call it before calling tdx_cpu_enable().  E.g., we
> can have below functions:
> 
> 1) tdx_global_init()	-> TDH_SYS_INIT
> 2) tdx_cpu_init()	-> TDH_SYS_LP_INIT
> 3) tdx_enable()		-> actual module initialization
> 
> How does this sound?

Ah, wait, I hadn't had enough wake-up juice, it's tdx_global_init() that
did the raw_spinlock_t, but that isn't the IPI thing.

Then perhaps just use a mutex to serialize things?