From: Matthew Wilcox <willy@infradead.org>
To: David Laight <David.Laight@aculab.com>
Cc: 'Tiezhu Yang' <yangtiezhu@loongson.cn>,
Dave Young <dyoung@redhat.com>, Baoquan He <bhe@redhat.com>,
Vivek Goyal <vgoyal@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-ia64@vger.kernel.org" <linux-ia64@vger.kernel.org>,
"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"linux-riscv@lists.infradead.org"
<linux-riscv@lists.infradead.org>,
"linux-sh@vger.kernel.org" <linux-sh@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Xuefeng Li <lixuefeng@loongson.cn>
Subject: Re: [PATCH v2 0/2] kdump: simplify code
Date: Mon, 13 Dec 2021 14:43:52 +0000 [thread overview]
Message-ID: <YbdcKK3Cq6ITTg/l@casper.infradead.org> (raw)
In-Reply-To: <b7a75ae9253445af81ff2fedd5268af4@AcuMS.aculab.com>
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.
next prev parent reply other threads:[~2021-12-13 14:44 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-11 3:33 [PATCH v2 0/2] kdump: simplify code Tiezhu Yang
2021-12-11 3:33 ` [PATCH v2 1/2] kdump: vmcore: remove copy_to() and add copy_to_user_or_kernel() Tiezhu Yang
2021-12-11 10:32 ` Christophe Leroy
2021-12-11 3:33 ` [PATCH v2 2/2] kdump: crashdump: use copy_to_user_or_kernel() to simplify code Tiezhu Yang
2021-12-11 17:53 ` [PATCH v2 0/2] kdump: " David Laight
2021-12-11 19:32 ` Christophe Leroy
2021-12-12 11:47 ` Matthew Wilcox
2021-12-13 8:30 ` David Laight
2021-12-13 14:43 ` Matthew Wilcox [this message]
2021-12-14 10:03 ` Tiezhu Yang
2021-12-14 13:14 ` Matthew Wilcox
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