From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751035AbdJAIEz (ORCPT <rfc822;w@1wt.eu>);
        Sun, 1 Oct 2017 04:04:55 -0400
Received: from verein.lst.de ([213.95.11.211]:59482 "EHLO newverein.lst.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1750980AbdJAIEv (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Sun, 1 Oct 2017 04:04:51 -0400
Date: Sun, 1 Oct 2017 10:04:49 +0200
From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: miles.chen@mediatek.com, Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Andrew Morton <akpm@linux-foundation.org>, wsd_upstream@mediatek.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        iommu@lists.linux-foundation.org, linux-mediatek@lists.infradead.org
Subject: Re: [PATCH v3] dma-debug: fix incorrect pfn calculation
Message-ID: <20171001080449.GB11843@lst.de>
References: <1506484087-1177-1-git-send-email-miles.chen@mediatek.com> <273077fd-c5ad-82c8-60aa-cde89355e5e8@arm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <273077fd-c5ad-82c8-60aa-cde89355e5e8@arm.com>
User-Agent: Mutt/1.5.17 (2007-11-01)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Sep 27, 2017 at 11:23:52AM +0100, Robin Murphy wrote:
> > I found that debug_dma_alloc_coherent() and debug_dma_free_coherent()
> > assume that dma_alloc_coherent() always returns a linear address.
> > However it's possible that dma_alloc_coherent() returns a non-linear
> > address. In this case, page_to_pfn(virt_to_page(virt)) will return an
> > incorrect pfn. If the pfn is valid and mapped as a COW page,
> > we will hit the warning when doing wp_page_copy().

Hmm, can the debug code assume anything?  Right now you're just patching
it from supporting linear and vmalloc.  But what about other
potential mapping types?

> > +	entry->pfn	 = is_vmalloc_addr(virt) ? vmalloc_to_pfn(virt) :
> > +						page_to_pfn(virt_to_page(virt));

Please use normal if/else conditionsals:

	if (is_vmalloc_addr(virt))
		entry->pfn = vmalloc_to_pfn(virt);
	else
		entry->pfn = page_to_pfn(virt_to_page(virt));

> > +		.pfn		= is_vmalloc_addr(virt) ? vmalloc_to_pfn(virt) :
> > +						page_to_pfn(virt_to_page(virt)),

Same here.