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Date:   Tue, 7 Dec 2021 12:15:26 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Christoph Hellwig <hch@lst.de>,
        Amit Daniel Kachhap <amit.kachhap@arm.com>,
        linux-kernel@vger.kernel.org,
        Vincenzo Frascino <Vincenzo.Frascino@arm.com>,
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        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        kexec <kexec@lists.infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Young <dyoung@redhat.com>, Baoquan He <bhe@redhat.com>,
        Vivek Goyal <vgoyal@redhat.com>, x86 <x86@kernel.org>
Subject: Re: [RFC PATCH 01/14] fs/proc/vmcore: Update read_from_oldmem()
 for user pointer
Message-ID: <20211207111526.GA18554@lst.de>
References: <20211203104231.17597-1-amit.kachhap@arm.com> <20211203104231.17597-2-amit.kachhap@arm.com> <20211206140451.GA4936@lst.de> <Ya4bdB0UBJCZhUSo@casper.infradead.org> <20211206145422.GA8794@lst.de> <Ya4nI7ly15pJA5xp@casper.infradead.org>
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On Mon, Dec 06, 2021 at 03:07:15PM +0000, Matthew Wilcox wrote:
> > > What do you think to adding a generic copy_pfn_to_iter()?  Not sure
> > > which APIs to use to implement it ... some architectures have weird
> > > requirements about which APIs can be used for what kinds of PFNs.
> > 
> > Hmm.  I though kmap_local_pfn(_prot) is all we need?
> 
> In the !HIGHMEM case, that calls pfn_to_page(), and I think the
> point of this path is that we don't have a struct page for this pfn.

Indeed.  But to me this suggest that the !highmem stub is broken and
we should probably fix it rather than adding yet another interface.