Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1432360AbdDYTSb (ORCPT ); Tue, 25 Apr 2017 15:18:31 -0400 Received: from mail.skyhub.de ([5.9.137.197]:34150 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S945674AbdDYTSX (ORCPT ); Tue, 25 Apr 2017 15:18:23 -0400 Date: Tue, 25 Apr 2017 21:18:09 +0200 From: Borislav Petkov To: Juergen Gross Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org, boris.ostrovsky@oracle.com, hpa@zytor.com, tglx@linutronix.de, mingo@redhat.com Subject: Re: [PATCH] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS if forced to zero Message-ID: <20170425191809.uvdt4jimnbvqbyf2@pd.tnic> References: <20170425180014.7533-1-jgross@suse.com> <20170425182443.3ab75tkfosol2yk4@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 630 Lines: 23 On Tue, Apr 25, 2017 at 08:34:34PM +0200, Juergen Gross wrote: > And what happens when there is a scheduling event right here? > __switch_to() will see X86_BUG_SYSRET_SS_ATTRS set and take a wrong > path. So the whole thing we're doing right now is wrong: set bit and then clear bit. We should not set the bit at all and there won't be any window to get it wrong. So can we do something like this instead: if (!cpu_has(c, X86_FEATURE_XENPV)) set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS); or is XENPV the wrong thing to test? -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.