linux-kernel - Re: [RFC PATCH 01/14] fs/proc/vmcore: Update read_from

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Message-ID: <20211206145422.GA8794@lst.de>
Date:   Mon, 6 Dec 2021 15:54:22 +0100
From:   Christoph Hellwig <hch@....de>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Christoph Hellwig <hch@....de>,
        Amit Daniel Kachhap <amit.kachhap@....com>,
        linux-kernel@...r.kernel.org,
        Vincenzo Frascino <Vincenzo.Frascino@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        kexec <kexec@...ts.infradead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>, x86 <x86@...nel.org>
Subject: Re: [RFC PATCH 01/14] fs/proc/vmcore: Update read_from_oldmem()
 for user pointer

On Mon, Dec 06, 2021 at 02:17:24PM +0000, Matthew Wilcox wrote:
> On Mon, Dec 06, 2021 at 03:04:51PM +0100, Christoph Hellwig wrote:
> > This looks like a huge mess.  What speak against using an iov_iter
> > here?
> 
> I coincidentally made a start on this last night.  Happy to stop.

Don't stop!

> 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?