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

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Message-ID: <7b61715ad35d7b9916f55df72378e02e62c5cc4e.camel@intel.com>
Date:   Wed, 28 Jun 2023 00:28:12 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.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 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?