linux-kernel - Re: [PATCHv3 09/17] x86/mm: Implement page_keyid() using page

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Date:   Mon, 18 Jun 2018 05:54:29 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Kai Huang <kai.huang@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv3 09/17] x86/mm: Implement page_keyid() using page_ext

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.