From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754363AbcB2Wh1 (ORCPT ); Mon, 29 Feb 2016 17:37:27 -0500 Received: from mail.skyhub.de ([78.46.96.112]:56195 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752868AbcB2WhZ (ORCPT ); Mon, 29 Feb 2016 17:37:25 -0500 Date: Mon, 29 Feb 2016 23:37:22 +0100 From: Borislav Petkov To: Brian Gerst Cc: Andy Lutomirski , Andy Lutomirski , X86 ML , "linux-kernel@vger.kernel.org" , Oleg Nesterov , Andrew Cooper Subject: Re: [PATCH 02/10] x86/entry/compat: In SYSENTER, sink AC clearing below the existing FLAGS test Message-ID: <20160229223722.GI3724@pd.tnic> References: <20160229203941.GG3724@pd.tnic> <20160229220903.GH3724@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 29, 2016 at 05:33:16PM -0500, Brian Gerst wrote: > SYSENTER doesn't save EFLAGS so we have to fudge it by pushing the > kernel's flags. Most user programs never set AC, so by adding it to > the test for flags to clear we can avoid the CLAC or POPF in the > common case that it is already clear. Yeah, Andy just explained it to me on IRC. Thanks guys. -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply.