From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 03E9D1A0010 for ; Mon, 11 May 2015 20:31:16 +1000 (AEST) In-Reply-To: <1430839821-9259-1-git-send-email-ldufour@linux.vnet.ibm.com> To: Laurent Dufour , linuxppc-dev@lists.ozlabs.org From: Michael Ellerman Subject: Re: powerpc: Enabling sys_kcmp for CRIU Message-Id: <20150511103115.DFE85140187@ozlabs.org> Date: Mon, 11 May 2015 20:31:15 +1000 (AEST) Cc: paulus@samba.org, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 2015-05-05 at 15:30:21 UTC, Laurent Dufour wrote: > The commit 8170a83f15ee ("powerpc: Wireup the kcmp syscall to sys_ni") has > disabled the kcmp syscall for powerpc. This has been done due to the use > of unsigned long parameters which may require a dedicated wrapper to handle > 32bit process on top of 64bit kernel. However in the kcmp() case, the 2 > unsigned long parameters are currently only used to carry file descriptors > from user space to the kernel. Since such a parameter is passed through > register, and file descriptor doesn't need to get extended, there is, > today, no need for a wrapper. > > In the case there will be a need to pass address in or out of this system > call, then a wrapper could be required, it will then be to care of it. > > As today this is not the case, it is safe to enable kcmp() on powerpc. That's mostly convincing. Though I see that s390 does have a compat wrapper, i386 doesn't. So who knows what that means. But, there's a selftest in tools/testing/selftests/kcmp. So can you run that as 32-bit and confirm it works? Then I'd be 100% convinced :) cheers