Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753249AbbDFSaw (ORCPT ); Mon, 6 Apr 2015 14:30:52 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:23994 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752726AbbDFSau (ORCPT ); Mon, 6 Apr 2015 14:30:50 -0400 Message-ID: <5522D0BC.80906@oracle.com> Date: Mon, 06 Apr 2015 14:30:20 -0400 From: Boris Ostrovsky User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Andrew Cooper , Andy Lutomirski , Konrad Rzeszutek Wilk CC: Denys Vlasenko , Denys Vlasenko , X86 ML , Linux Kernel Mailing List , Borislav Petkov , Andy Lutomirski , "H. Peter Anvin" , "xen-devel@lists.xenproject.org" , Linus Torvalds , Ingo Molnar Subject: Re: [Xen-devel] [PATCH] x86, paravirt, xen: Remove the 64-bit irq_enable_sysexit pvop References: <8a03355698fe5b94194e9e7360f19f91c1b2cf1f.1428100853.git.luto@kernel.org> <20150406141051.GF12596@l.oracle.com> <5522C5EA.8060803@citrix.com> In-Reply-To: <5522C5EA.8060803@citrix.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1922 Lines: 45 On 04/06/2015 01:44 PM, Andrew Cooper wrote: > On 06/04/2015 16:29, Andy Lutomirski wrote: >> On Mon, Apr 6, 2015 at 7:10 AM, Konrad Rzeszutek Wilk >> wrote: >>> On Fri, Apr 03, 2015 at 03:52:30PM -0700, Andy Lutomirski wrote: >>>> [cc: Boris and Konrad. Whoops] >>>> >>>> On Fri, Apr 3, 2015 at 3:51 PM, Andy Lutomirski wrote: >>>>> We don't use irq_enable_sysexit on 64-bit kernels any more. Remove >>> Is there an commit (or name of patch) that explains why 32-bit-user-space-on-64-bit >>> kernels is unsavory? >> sysexit never tasted very good :-p >> >> We're (hopefully) not breaking 32-bit-user-space-on-64-bit, but we're >> trying an unconventional approach to making the code faster and less >> scary. As a result, 64-bit kernels won't use sysexit any more. >> Hopefully Xen is okay with the slightly sneaky thing we're doing. >> AFAICT Xen thinks of sysretl and sysexit as slightly funny irets, so I >> don't expect there to be any problem. > 64bit PV kernels must bounce through Xen to switch from the kernel to > the user pagetables (since both kernel and userspace are both actually > running in ring3 with user pages). > > As a result, exit to userspace ends up as a hypercall into Xen which has > an effect very similar to an `iret`, but with some extra fixup in the > background. > > I can't forsee any Xen issues as a result of this patch. I ran tip plus this patch (plus another patch that fixes an unrelated Xen regression in tip) through our test suite and it completed without problems. I also ran some very simple 32-bit programs in a 64-bit PV guest and didn't see any problems there neither. -boris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/