Re: [PATCHv3 09/17] x86/mm: Implement page_keyid() using page_ext

Kirill A. Shutemov
2018-06-18T13:14:10Z

On Mon, Jun 18, 2018 at 12:54:29PM +0000, Dave Hansen wrote:
> On 06/18/2018 03:07 AM, Kirill A. Shutemov wrote:
> > On Wed, Jun 13, 2018 at 06:20:10PM +0000, Dave Hansen wrote:
> >>> +int page_keyid(const struct page *page)
> >>> +{
> >>> + if (mktme_status != MKTME_ENABLED)
> >>> + return 0;
> >>> +
> >>> + return lookup_page_ext(page)->keyid;
> >>> +}
> >>> +EXPORT_SYMBOL(page_keyid);
> >> Please start using a proper X86_FEATURE_* flag for this. It will give
> >> you all the fancy static patching that you are missing by doing it this way.
> > There's no MKTME CPU feature.
>
> Right. We have tons of synthetic features that have no basis in the
> hardware CPUID feature.
>
> > Well, I guess we can invent syntactic one or just use static key directly.
>
> Did you mean synthetic?

Right.

> > Let's see how it behaves performance-wise before optimizing this.
>
> It's not an optimization, it's how we do things in arch/x86, and it has
> a *ton* of optimization infrastructure behind it that you get for free
> if you use it.
>
> I'm just trying to save Thomas's tired fingers from having to say the
> same thing in a week or two when he looks at this.

Okay, I'll look into this.

--
Kirill A. Shutemov