Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753953AbbFCJg5 (ORCPT ); Wed, 3 Jun 2015 05:36:57 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:15393 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752511AbbFCJgt (ORCPT ); Wed, 3 Jun 2015 05:36:49 -0400 X-IronPort-AV: E=Sophos;i="5.13,546,1427760000"; d="scan'208";a="271179384" From: Andrew Cooper To: Xen-devel CC: David Vrabel , Rusty Russell , Andrew Cooper , "Thomas Gleixner" , Ingo Molnar , "H. Peter Anvin" , , , Konrad Rzeszutek Wilk , Boris Ostrovsky , , Subject: [PATCH] x86/cpu: Fix SMAP check in PVOPS environments Date: Wed, 3 Jun 2015 10:31:14 +0100 Message-ID: <1433323874-6927-1-git-send-email-andrew.cooper3@citrix.com> X-Mailer: git-send-email 1.7.10.4 MIME-Version: 1.0 Content-Type: text/plain X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2176 Lines: 56 There appears to be no formal statement of what pv_irq_ops.save_fl() is supposed to return precisely. Native returns the full flags, while lguest and Xen only return the Interrupt Flag, and both have comments by the implementations stating that only the Interrupt Flag is looked at. This may have been true when initially implemented, but no longer is. To make matters worse, the Xen PVOP leaves the upper bits undefined, making the BUG_ON() undefined behaviour. Experimentally, this now trips for 32bit PV guests on Broadwell hardware. The BUG_ON() is consistent for an individual build, but not consistent for all builds. It has also been a sitting timebomb since SMAP support was introduced. Use native_save_fl() instead, which will obtain an accurate view of the AC flag. Signed-off-by: Andrew Cooper Reviewed-by: David Vrabel Tested-by: Rusty Russell CC: Thomas Gleixner CC: Ingo Molnar CC: H. Peter Anvin CC: x86@kernel.org CC: linux-kernel@vger.kernel.org CC: Konrad Rzeszutek Wilk CC: Boris Ostrovsky CC: xen-devel CC: lguest@lists.ozlabs.org CC: stable@vger.kernel.org --- arch/x86/kernel/cpu/common.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index a62cf04..4f2fded 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -291,10 +291,9 @@ __setup("nosmap", setup_disable_smap); static __always_inline void setup_smap(struct cpuinfo_x86 *c) { - unsigned long eflags; + unsigned long eflags = native_save_fl(); /* This should have been cleared long ago */ - raw_local_save_flags(eflags); BUG_ON(eflags & X86_EFLAGS_AC); if (cpu_has(c, X86_FEATURE_SMAP)) { -- 1.7.10.4 -- 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/