linux-kernel - Re: [PATCH v2 0/2] kdump: simplify code

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Date:   Tue, 14 Dec 2021 13:14:48 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     David Laight <David.Laight@...lab.com>,
        Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [PATCH v2 0/2] kdump: simplify code

On Tue, Dec 14, 2021 at 06:03:11PM +0800, Tiezhu Yang wrote:
> On 12/13/2021 10:43 PM, Matthew Wilcox wrote:
> > On Mon, Dec 13, 2021 at 08:30:33AM +0000, David Laight wrote:
> > > From: Matthew Wilcox
> > > > Sent: 12 December 2021 11:48
> > > > 
> > > > On Sat, Dec 11, 2021 at 05:53:46PM +0000, David Laight wrote:
> > > > > From: Tiezhu Yang
> > > > > > Sent: 11 December 2021 03:33
> > > > > > 
> > > > > > v2:
> > > > > >   -- add copy_to_user_or_kernel() in lib/usercopy.c
> > > > > >   -- define userbuf as bool type
> > > > > 
> > > > > Instead of having a flag to indicate whether the buffer is user or kernel,
> > > > > would it be better to have two separate buffer pointers.
> > > > > One for a user space buffer, the other for a kernel space buffer.
> > > > > Exactly one of the buffers should always be NULL.
> > > > 
> > > > No.  You should be using an iov_iter instead.  See
> > > > https://lore.kernel.org/all/Ya4bdB0UBJCZhUSo@casper.infradead.org/
> > > > for a start on this.
> > > 
> > > iov_iter gets horribly expensive...
> > 
> > Oh, right.  Reading the kcore is a high-performance path, my mistake.
> > 
> 
> Hi,
> 
> Thank you for your discussions.
> 
> The intention of this patchset is to simplify the related code with no
> functional changes and no side effects.
> 
> At this moment, if you are OK, I will send v3 used with inline function
> copy_to_user_or_kernel() to keep it simple, maybe other more changes can
> be done in the future if no any side effect.

That would be pointless.  I already sent a series to remove this,
which you were cc'd on.