Re: [PATCH v10 08/11] x86/tdx: Wire up KVM hypercalls

[Sathyanarayanan Kuppuswamy]

On 10/14/21 3:21 AM, Thomas Gleixner wrote:
> On Fri, Oct 08 2021 at 22:37, Kuppuswamy Sathyanarayanan wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> >   
> >   #ifdef CONFIG_KVM_GUEST
> > @@ -32,6 +34,10 @@ static inline bool kvm_check_and_clear_guest_paused(void)
> >   static inline long kvm_hypercall0(unsigned int nr)
> >   {
> >   	long ret;
> > +
> > +	if (cc_platform_has(CC_ATTR_GUEST_TDX))
> > +		return tdx_kvm_hypercall(nr, 0, 0, 0, 0);
> So if TDX is not enabled in Kconfig this cannot be optimized out unless
> CC_PLATFORM is disabled as well. But what's worse is that every
> hypercall needs to call into cc_platform_has().
>
> None of the hypercalls is used before the early TDX detection. So we can
> simply use
>
>         if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
>
> here, right? Then you add X86_FEATURE_TDX_GUEST to the disabled feature
> bits correctly and all of the above is solved.
>
> Hmm?


Make sense. Since this will only be used after tdx_early_init() call,
and X86_FEATURE_TDX_GUEST is also set in that call, we can just use
cpu_feature_enabled(X86_FEATURE_TDX_GUEST) as you have mentioned.

I will fix this in next version.

>   
> > +#if defined(CONFIG_KVM_GUEST) && defined(CONFIG_INTEL_TDX_GUEST)
> > +static inline long tdx_kvm_hypercall(unsigned int nr, unsigned long p1,
> > +				     unsigned long p2, unsigned long p3,
> > +				     unsigned long p4)
> > +{
> > +	struct tdx_hypercall_output out;
> > +	u64 err;
> > +
> > +	err = __tdx_hypercall(TDX_HYPERCALL_VENDOR_KVM, nr, p1, p2,
> > +			      p3, p4, &out);
> > +
> > +	/*
> > +	 * Non zero return value means buggy TDX module (which is fatal).
> > +	 * So use BUG_ON() to panic.
> > +	 */
> > +	BUG_ON(err);
> > +
> > +	return out.r10;
> > +}
> Can we make that a proper exported function (instead of
> tdx_kvm_hypercall) so we don't end up with the very same code inlined
> all over the place?


Initially it was an exported function. But we made it inline in tdx.h
to simplify the implementation. But if exported function is preferred,
I will fix it in next version.

> Thanks,
>
>          tglx
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer