linux-kernel - Re: [PATCH v6 04/11] swiotlb: Map the buffer if it was unmapped by XPFO

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Date:   Thu, 7 Sep 2017 11:10:15 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Tycho Andersen <tycho@...ker.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>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v6 04/11] swiotlb: Map the buffer if it was unmapped by
 XPFO

> -	if (PageHighMem(pfn_to_page(pfn))) {
> +	if (PageHighMem(page) || xpfo_page_is_unmapped(page)) {

Please don't sprinkle xpfo details over various bits of code.

Just add a helper with a descriptive name, e.g.

page_is_unmapped()

that also includes the highmem case, as that will easily document
what this check is doing.