Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752794AbbD3TSD (ORCPT ); Thu, 30 Apr 2015 15:18:03 -0400 Received: from mail-lb0-f169.google.com ([209.85.217.169]:33343 "EHLO mail-lb0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752170AbbD3TR5 (ORCPT ); Thu, 30 Apr 2015 15:17:57 -0400 MIME-Version: 1.0 In-Reply-To: <1430420925-20474-1-git-send-email-boris.ostrovsky@oracle.com> References: <1430420925-20474-1-git-send-email-boris.ostrovsky@oracle.com> From: Andy Lutomirski Date: Thu, 30 Apr 2015 12:17:35 -0700 Message-ID: Subject: Re: [PATCH] hypervisor/x86/xen: Unset X86_BUG_SYSRET_SS_ATTRS on Xen PV guests To: Boris Ostrovsky Cc: Konrad Rzeszutek Wilk , David Vrabel , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , "linux-kernel@vger.kernel.org" , "xen-devel@lists.xenproject.org" , linux@eikelenboom.it 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: 1035 Lines: 25 On Thu, Apr 30, 2015 at 12:08 PM, Boris Ostrovsky wrote: > Commit 61f01dd941ba ("x86_64, asm: Work around AMD SYSRET SS descriptor > attribute issue") makes AMD processors set SS to __KERNEL_DS in > __switch_to() to deal with cases when SS is NULL. > > This breaks Xen PV guests who do not want to load SS with__KERNEL_DS. > > Since the problem that the commit is trying to address would have to be > fixed in the hypervisor (if it in fact exists under Xen) there is no > reason to set X86_BUG_SYSRET_SS_ATTRS flag for PV VPCUs here. > Seems reasonable. Have you run the test case on a Xen PV guest on AMD? It's possible that Xen is affected, since the old accidental workaround that we deleted was in the vdso and probably would have worked on Xen. --Andy -- 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/