Re: [PATCH v3 10/11] mm: x86: Invoke hypercall when page encryption status is changed

[Thomas Gleixner]

On Thu, 29 Aug 2019, Thomas Gleixner wrote:
> On Thu, 29 Aug 2019, Borislav Petkov wrote:
> 
> > On Wed, Jul 10, 2019 at 08:13:11PM +0000, Singh, Brijesh wrote:
> > > @@ -2060,6 +2067,14 @@ static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
> > >  	 */
> > >  	cpa_flush(&cpa, 0);
> > >  
> > > +	/*
> > > +	 * When SEV is active, notify hypervisor that a given memory range is mapped
> > > +	 * encrypted or decrypted. Hypervisor will use this information during
> > > +	 * the VM migration.
> > > +	 */
> > > +	if (sev_active())
> > > +		set_memory_enc_dec_hypercall(addr, numpages << PAGE_SHIFT, enc);
> > 
> > Btw, tglx has a another valid design concern here: why isn't this a
> > pv_ops thing? So that it is active only when the hypervisor is actually
> > present?
> > 
> > I know, I know, this will run on SEV guests only because it is all
> > (hopefully) behind "if (sev_active())" checks but the clean and accepted
> > design is a paravirt call, I'd say.
> 
> No. sev_active() has nothing to do with guest mode. It tells whether SEV is
> active or not. So yes, this calls into this function on both guest and
> host. The latter is beyond pointless.

Oops. sme != sev.

But yes, can we please hide that a bit better....