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Subject: Re: [PATCHv2 12/14] x86/mm: Implement page_keyid() using page_ext
References: <20180328165540.648-1-kirill.shutemov@linux.intel.com>
 <20180328165540.648-13-kirill.shutemov@linux.intel.com>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <b4498b2b-5092-b347-e92d-6ebd375fd947@intel.com>
Date: Wed, 28 Mar 2018 09:59:23 -0700
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Sender: owner-linux-mm@kvack.org
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Ingo Molnar <mingo@redhat.com>, x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>, Tom Lendacky <thomas.lendacky@amd.com>
Cc: Kai Huang <kai.huang@linux.intel.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org

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?