Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753914AbbDFUDq (ORCPT ); Mon, 6 Apr 2015 16:03:46 -0400 Received: from mail-la0-f41.google.com ([209.85.215.41]:33960 "EHLO mail-la0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752789AbbDFUDm (ORCPT ); Mon, 6 Apr 2015 16:03:42 -0400 MIME-Version: 1.0 In-Reply-To: <5522D0BC.80906@oracle.com> References: <8a03355698fe5b94194e9e7360f19f91c1b2cf1f.1428100853.git.luto@kernel.org> <20150406141051.GF12596@l.oracle.com> <5522C5EA.8060803@citrix.com> <5522D0BC.80906@oracle.com> From: Andy Lutomirski Date: Mon, 6 Apr 2015 13:03:19 -0700 Message-ID: Subject: Re: [Xen-devel] [PATCH] x86, paravirt, xen: Remove the 64-bit irq_enable_sysexit pvop To: Boris Ostrovsky Cc: Andrew Cooper , Konrad Rzeszutek Wilk , 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 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2300 Lines: 69 On Mon, Apr 6, 2015 at 11:30 AM, Boris Ostrovsky wrote: > > 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. At the risk of redundancy, did you test on Intel hardware? At least on native systems, the code in question never executes on AMD systems. --Andy > > -boris > -- Andy Lutomirski AMA Capital Management, LLC -- 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/