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Subject: Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame
 Ownership (XPFO)
References: <20170907173609.22696-1-tycho@docker.com>
 <20170907173609.22696-4-tycho@docker.com>
From: Laura Abbott <labbott@redhat.com>
Message-ID: <d4935027-aca6-f7a2-d15b-50b94484ecaf@redhat.com>
Date: Sat, 9 Sep 2017 08:35:17 -0700
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Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Tycho Andersen <tycho@docker.com>, linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, kernel-hardening@lists.openwall.com, Marco Benatto <marco.antonio.780@gmail.com>, Juerg Haefliger <juerg.haefliger@canonical.com>, x86@kernel.org

On 09/07/2017 10:36 AM, Tycho Andersen wrote:
> +static inline struct xpfo *lookup_xpfo(struct page *page)
> +{
> +	struct page_ext *page_ext = lookup_page_ext(page);
> +
> +	if (unlikely(!page_ext)) {
> +		WARN(1, "xpfo: failed to get page ext");
> +		return NULL;
> +	}
> +
> +	return (void *)page_ext + page_xpfo_ops.offset;
> +}
> +

Just drop the WARN. On my arm64 UEFI machine this spews warnings
under most normal operation. This should be normal for some
situations but I haven't had the time to dig into why this
is so pronounced on arm64.

Thanks,
Laura

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