From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1042516AbdDUWBY (ORCPT ); Fri, 21 Apr 2017 18:01:24 -0400 Received: from mail-oi0-f67.google.com ([209.85.218.67]:34325 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1042444AbdDUWBU (ORCPT ); Fri, 21 Apr 2017 18:01:20 -0400 MIME-Version: 1.0 In-Reply-To: <20170420192446.GS29622@ZenIV.linux.org.uk> References: <20170420175549.3435196-1-arnd@arndb.de> <20170420192446.GS29622@ZenIV.linux.org.uk> From: Arnd Bergmann Date: Sat, 22 Apr 2017 00:01:19 +0200 X-Google-Sender-Auth: Zf7y6r-XhZqNIdtsuXsM8jgSWQc Message-ID: Subject: Re: [PATCH 1/4] scsi: pmcraid: use __iomem pointers for ioctl argument To: Al Viro Cc: "James E.J. Bottomley" , "Martin K. Petersen" , Johannes Berg , linux-scsi@vger.kernel.org, Linux Kernel Mailing List Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 20, 2017 at 9:24 PM, Al Viro wrote: > On Thu, Apr 20, 2017 at 07:54:45PM +0200, Arnd Bergmann wrote: >> kernelci.org reports a new compile warning for old code in the pmcraid >> driver: >> >> arch/mips/include/asm/uaccess.h:138:21: warning: passing argument 1 of '__access_ok' makes pointer from integer without a cast [-Wint-conversion] >> >> The warning got introduced by a cleanup to the access_ok() helper >> that requires the argument to be a pointer, where the old version >> silently accepts 'unsigned long' arguments as it still does on most >> other architectures. >> >> The new behavior in MIPS however seems absolutely sensible, and so far I >> could only find one other file with the same issue, so the best solution >> seems to be to clean up the pmcraid driver. >> >> This makes the driver consistently use 'void __iomem *' pointers for >> passing around the address of the user space ioctl arguments, which gets >> rid of the kernelci warning as well as several sparse warnings. > > Is there any point in keeping that access_ok() in the first place, rather > than just switching to copy_from_user()/copy_to_user() in there? AFAICS, > it's only for the sake of the loop in pmcraid_copy_sglist(): > for (i = 0; i < (len / bsize_elem); i++, buffer += bsize_elem) { > struct page *page = sg_page(&scatterlist[i]); > > kaddr = kmap(page); > if (direction == DMA_TO_DEVICE) > rc = __copy_from_user(kaddr, > (void *)buffer, > bsize_elem); > else > rc = __copy_to_user((void *)buffer, kaddr, bsize_elem); > > kunmap(page); > > if (rc) { > pmcraid_err("failed to copy user data into sg list\n"); > return -EFAULT; > } > > scatterlist[i].length = bsize_elem; > } > and seeing that each of those calls copies is at least a full page... If > there is an architecture where a single access_ok() costs a noticable fraction > of the time it takes to copy a full page, we have a much worse problem than > overhead in obscure ioctl... Right, that would also fix the warning. I think we should just do both fixes, as they are each a worthwhile cleanup. I can do this as another patch on top of the series. I've done that second patch now and given it a spin on the randconfig test builds. Arnd