Re: [PATCHv2 12/14] x86/mm: Implement page_keyid() using page_ext

[Kirill A. Shutemov]

On Wed, Mar 28, 2018 at 09:59:23AM -0700, Dave Hansen wrote:
> On 03/28/2018 09:55 AM, Kirill A. Shutemov wrote:
> > +static inline int page_keyid(struct page *page)
> > +{
> > +	if (!mktme_nr_keyids)
> > +		return 0;
> > +
> > +	return lookup_page_ext(page)->keyid;
> > +}
> 
> This doesn't look very optimized.  Don't we normally try to use
> X86_FEATURE_* for these checks so that we get the runtime patching *and*
> compile-time optimizations?

I didn't go to micro optimization just yet. I would like to see whole
stack functioning first.

It doesn't make sense to use cpu_feature_enabledX86_FEATURE_TME) as it
would produce false-positives: MKTME enumeration requires MSR read.

We may change mktme_nr_keyids check to a static key here. But this is not
urgent.

-- 
 Kirill A. Shutemov