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

Dave Hansen
2018-06-18T12:54:34Z

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?

> 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.