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 14:55:21 +0300
From:   "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Huang, Ying" <ying.huang@...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>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "nik.borisov@...e.com" <nik.borisov@...e.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Luck, Tony" <tony.luck@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>, "bp@...en8.de" <bp@...en8.de>,
        "Brown, Len" <len.brown@...el.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v12 07/22] x86/virt/tdx: Add skeleton to enable TDX on
 demand

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.
> 	 */
> 
> This allows a use case that the caller simply wants to call some SEAMCALL on
> local cpu, e.g., IOMMU code may just use below to get some TDX-IO information:
> 
> 	preempt_disable();
> 	vmxon();
> 	tdx_cpu_enable();
> 	SEAMCALL;
> 	vmxoff();
> 	preempt_enable();
> 
> Are you OK with this?

Is it hypothetical use-case? If so, I would rather keep it simple for now
and adjust in the future if needed.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov