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

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Date:   Thu, 8 Jun 2023 06:43:29 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Huang, Kai" <kai.huang@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "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>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "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 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.




>>> +int tdx_cpu_enable(void)
>>> +{
>>> +   unsigned int lp_status;
>>> +   int ret;
>>> +
>>> +   if (!platform_tdx_enabled())
>>> +           return -EINVAL;
>>> +
>>> +   lp_status = __this_cpu_read(tdx_lp_init_status);
>>> +
>>> +   /* Already done */
>>> +   if (lp_status & TDX_LP_INIT_DONE)
>>> +           return lp_status & TDX_LP_INIT_FAILED ? -EINVAL : 0;
>>> +
>>> +   /*
>>> +    * The TDX module global initialization is the very first step
>>> +    * to enable TDX.  Need to do it first (if hasn't been done)
>>> +    * before doing the per-cpu initialization.
>>> +    */
>>> +   ret = try_init_module_global();
>>> +
>>> +   /*
>>> +    * If the module global initialization failed, there's no point
>>> +    * to do the per-cpu initialization.  Just mark it as done but
>>> +    * failed.
>>> +    */
>>> +   if (ret)
>>> +           goto update_status;
>>> +
>>> +   /* All '0's are just unused parameters */
>>> +   ret = seamcall(TDH_SYS_LP_INIT, 0, 0, 0, 0, NULL, NULL);
>>> +
>>> +update_status:
>>> +   lp_status = TDX_LP_INIT_DONE;
>>> +   if (ret)
>>> +           lp_status |= TDX_LP_INIT_FAILED;
>>> +
>>> +   this_cpu_write(tdx_lp_init_status, lp_status);
>>> +
>>> +   return ret;
>>> +}
>>> +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.