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Date:   Sun, 6 Oct 2019 23:13:24 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Alan Mikhak <alan.mikhak@sifive.com>
Cc:     linux-kernel@vger.kernel.org, martin.petersen@oracle.com,
        alexios.zavras@intel.com, ming.lei@redhat.com,
        gregkh@linuxfoundation.org, tglx@linutronix.de, jgg@ziepe.ca,
        christophe.leroy@c-s.fr, palmer@sifive.com,
        paul.walmsley@sifive.com
Subject: Re: [PATCH] scatterlist: Validate page before calling PageSlab()
Message-ID: <20191007061324.GB17978@infradead.org>
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On Mon, Sep 30, 2019 at 04:22:35PM -0700, Alan Mikhak wrote:
> From: Alan Mikhak <alan.mikhak@sifive.com>
> 
> Modify sg_miter_stop() to validate the page pointer
> before calling PageSlab(). This check prevents a crash
> that will occur if PageSlab() gets called with a page
> pointer that is not backed by page struct.
> 
> A virtual address obtained from ioremap() for a physical
> address in PCI address space can be assigned to a
> scatterlist segment using the public scatterlist API
> as in the following example:

As Jason pointed out that is not a valid use of scatterlist.  What
are you trying to do here at a higher level?