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

[Huang, Kai]

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!