linux-kernel - Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame Ownership (XPFO)

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Date:   Mon, 11 Sep 2017 08:03:42 -0700
From:   Tycho Andersen <tycho@...ker.com>
To:     Laura Abbott <labbott@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kernel-hardening@...ts.openwall.com,
        Marco Benatto <marco.antonio.780@...il.com>,
        Juerg Haefliger <juerg.haefliger@...onical.com>, x86@...nel.org
Subject: Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame
 Ownership (XPFO)

On Sat, Sep 09, 2017 at 08:35:17AM -0700, Laura Abbott wrote:
> 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.

Will do, thanks! If you figure out under what conditions it's normal,
I'd be curious :)

Tycho