linux-kernel - Re: [PATCHv2 12/14] x86/mm: Implement page_keyid() using page

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Message-ID: <b4498b2b-5092-b347-e92d-6ebd375fd947@intel.com>
Date:   Wed, 28 Mar 2018 09:59:23 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     Kai Huang <kai.huang@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 12/14] x86/mm: Implement page_keyid() using page_ext

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?