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

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Message-ID: <03def8b40a7db14f31d2ad67fb1a201e8ae8bce0.camel@intel.com>
Date:   Thu, 29 Jun 2023 00:15:13 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "peterz@...radead.org" <peterz@...radead.org>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.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>,
        "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>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
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        "Shahar, Sagi" <sagis@...gle.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Gao, Chao" <chao.gao@...el.com>
Subject: Re: [PATCH v12 07/22] x86/virt/tdx: Add skeleton to enable TDX on
 demand

On Wed, 2023-06-28 at 15:35 +0200, Peter Zijlstra wrote:
> On Wed, Jun 28, 2023 at 12:28:12AM +0000, Huang, Kai wrote:
> > On Tue, 2023-06-27 at 22:37 +0000, Huang, Kai wrote:
> > > > > 
> > > > > +/*
> > > > > + * Do the module global initialization if not done yet.
> > > > > + * It's always called with interrupts and preemption disabled.
> > > > > + */
> > > > 
> > > > If interrupts are always disabled why do you need _irqsave()?
> > > > 
> > > 
> > > I'll remove the _irqsave().
> > > 
> > > AFAICT Isaku preferred this for additional security, but this is not
> > > necessary.
> > > 
> > > 
> > 
> > Damn.  I think we can change the comment to say this function is called with
> > preemption being disabled, but _can_ be called with interrupt disabled.  And we
> > keep using the _irqsave() version.
> > 
> > 	/*
> > 	 * Do the module global initialization if not done yet.  It's always
> > 	 * called with preemption disabled and can be called with interrupts
> > 	 * disabled.
> > 	 */
> 
> That's still not explaining *why*, what you want to say is:
> 
> 	Can be called locally or through an IPI function call.
> 

Thanks.  As in another reply, if using spinlock is OK, then I think we can say
it will be called either locally or through an IPI function call.  Otherwise, we
do via a new separate function tdx_global_init() and no lock is needed in that
function.  The caller should call it properly.