From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755136Ab2JGX4A (ORCPT ); Sun, 7 Oct 2012 19:56:00 -0400 Received: from terminus.zytor.com ([198.137.202.10]:38423 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751334Ab2JGXz6 (ORCPT ); Sun, 7 Oct 2012 19:55:58 -0400 User-Agent: K-9 Mail for Android In-Reply-To: <1349645172.16173.152.camel@deadeye.wl.decadent.org.uk> References: <20120928182957.993484211@linuxfoundation.org> <20120928183018.599659336@linuxfoundation.org> <1349645172.16173.152.camel@deadeye.wl.decadent.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: [ 174/262] x86, avx: dont use avx instructions with "noxsave" boot param From: "H. Peter Anvin" Date: Mon, 08 Oct 2012 07:55:31 +0800 To: Ben Hutchings , Suresh Siddha CC: linux-kernel@vger.kernel.org, stable@vger.kernel.org, alan@lxorguk.ukuu.org.uk, Greg Kroah-Hartman Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Userland should use a different query mechanism. On the other hand, it will not hurt either. On pre-xsave kernels AVX is a non-option. Ben Hutchings wrote: >On Fri, 2012-09-28 at 11:51 -0700, Greg Kroah-Hartman wrote: >> From: Greg KH >> >> 3.5-stable review patch. If anyone has any objections, please let me >know. >> >> ------------------ >> >> From: Suresh Siddha >> >> commit c6fd893da927c6cefb2ece22402765379921a834 upstream. >> >> Clear AVX, AVX2 features along with clearing XSAVE feature bits, >> as part of the parsing "noxsave" parameter. >> >> Fixes the kernel boot panic with "noxsave" boot parameter. >> >> We could have checked cpu_has_osxsave along with cpu_has_avx etc, but >Peter >> mentioned clearing the feature bits will be better for uses like >> static_cpu_has() etc. > >This was marked as needed for 3.5 only - presumably because the kernel >wasn't using AVX before this - but don't we also need to clear these >bits even in earlier versions so userland knows not to use it? > >Ben. > >> Signed-off-by: Suresh Siddha >> Link: >http://lkml.kernel.org/r/1343755754.2041.2.camel@sbsiddha-desk.sc.intel.com >> Signed-off-by: H. Peter Anvin >> Signed-off-by: Greg Kroah-Hartman >> >> --- >> arch/x86/kernel/cpu/common.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> --- a/arch/x86/kernel/cpu/common.c >> +++ b/arch/x86/kernel/cpu/common.c >> @@ -144,6 +144,8 @@ static int __init x86_xsave_setup(char * >> { >> setup_clear_cpu_cap(X86_FEATURE_XSAVE); >> setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT); >> + setup_clear_cpu_cap(X86_FEATURE_AVX); >> + setup_clear_cpu_cap(X86_FEATURE_AVX2); >> return 1; >> } >> __setup("noxsave", x86_xsave_setup); -- Sent from my mobile phone. Please excuse brevity and lack of formatting.