Re: [PATCH 4/8] x86/traps: Demand-populate PASID MSR via #GP

[Peter Zijlstra]

On Thu, Sep 23, 2021 at 10:14:42AM -0700, Luck, Tony wrote:
> On Wed, Sep 22, 2021 at 11:07:22PM +0200, Peter Zijlstra wrote:
> > On Mon, Sep 20, 2021 at 07:23:45PM +0000, Fenghua Yu wrote:
> > > @@ -538,6 +547,9 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
> > >  
> > >  	cond_local_irq_enable(regs);
> > >  
> > > +	if (user_mode(regs) && fixup_pasid_exception())
> > > +		goto exit;
> > > +
> 
> > So you're eating any random #GP that might or might not be PASID
> > related. And all that witout a comment... Enlighten?
> 
> This is moderately well commented inside the fixup_pasid_exception()
> function. Another copy of the comments here at the call-site seems
> overkill.

+static bool fixup_pasid_exception(void)
+{
+       if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
+               return false;
+
+       return __fixup_pasid_exception();
+}

/me goes looking for comments in that function, lemme get out the
electron microscope, because I can't seem to spot them with the naked
eye.