From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Date: Mon, 13 Dec 2021 14:43:52 +0000 Subject: Re: [PATCH v2 0/2] kdump: simplify code Message-Id: List-Id: References: <1639193588-7027-1-git-send-email-yangtiezhu@loongson.cn> <0c5cb37139af4f3e85cc2c5115d7d006@AcuMS.aculab.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: David Laight Cc: 'Tiezhu Yang' , Dave Young , Baoquan He , Vivek Goyal , Andrew Morton , "linux-arm-kernel@lists.infradead.org" , "linux-ia64@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-riscv@lists.infradead.org" , "linux-sh@vger.kernel.org" , "x86@kernel.org" , "linux-fsdevel@vger.kernel.org" , "kexec@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Xuefeng Li 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.