linux-kernel - Re: [PATCH v11 07/20] x86/virt/tdx: Add skeleton to enable TDX on demand

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Message-ID: <6db6e4fc876442715723b9c2f8f0d374f9343c76.camel@intel.com>
Date:   Mon, 12 Jun 2023 11:21:55 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "Luck, Tony" <tony.luck@...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>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v11 07/20] x86/virt/tdx: Add skeleton to enable TDX on
 demand

On Thu, 2023-06-08 at 06:43 -0700, Dave Hansen wrote:
> On 6/7/23 19:10, Huang, Kai wrote:
> > On Wed, 2023-06-07 at 08:22 -0700, Dave Hansen wrote:
> > > On 6/4/23 07:27, 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);
> > > 
> > > Why is this "raw_"?
> > > 
> > > There's zero mention of it anywhere.
> > 
> > Isaku pointed out the normal spinlock_t is converted to sleeping lock for
> > PREEMPT_RT kernel.  KVM calls this with IRQ disabled, thus requires a non-
> > sleeping lock.
> > 
> > How about adding below comment here?
> > 
> >         /*
> >          * Normal spinlock_t is converted to sleeping lock in PREEMPT_RT
> >          * kernel.  Use raw_spinlock_t instead so this function can be called
> >          * even when IRQ is disabled in any kernel configuration.
> >          */
> 
> Go look at *EVERY* *OTHER* raw_spinlock_t in the kernel.  Do any of them
> say this?
> 
> Comment the function, say that it's always called with interrupts and
> preempt disabled.  Leaves it at that.  *Maybe* add on that it needs raw
> spinlocks because of it.  But don't (try to) explain the background of
> the lock type.
> 

Thanks.  Will do, with one minor:

I'd like to replace "it's always called with interrupts and preempt disabled"
with "it can be called with interrupts disabled", because in the future non-KVM
code may call this when interrupt is enabled but preemption is disabled.

[...]

> > > > +EXPORT_SYMBOL_GPL(tdx_cpu_enable);
> > > 
> > > You danced around it in the changelog, but the reason for the exports is
> > > not clear.
> > 
> > I'll add one sentence to the changelog to explain:
> > 
> >         Export both tdx_cpu_enable() and tdx_enable() as KVM will be the kernel
> >         component to use TDX.
> 
> Intel doesn't pay me by the word.  Do you get paid that way?  If not,
> please just say:
> 
> 	Export both tdx_cpu_enable() and tdx_enable() for KVM use.

Thanks!