From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934005AbYDQB3c (ORCPT ); Wed, 16 Apr 2008 21:29:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760963AbYDQBJv (ORCPT ); Wed, 16 Apr 2008 21:09:51 -0400 Received: from sous-sol.org ([216.99.217.87]:59020 "EHLO sous-sol.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762116AbYDQBJu (ORCPT ); Wed, 16 Apr 2008 21:09:50 -0400 Message-Id: <20080417010326.442366326@sous-sol.org> References: <20080417010122.148289106@sous-sol.org> User-Agent: quilt/0.46-1 Date: Wed, 16 Apr 2008 18:01:35 -0700 From: Chris Wright To: linux-kernel@vger.kernel.org, stable@kernel.org, jejb@kernel.org Cc: Justin Forbes , Zwane Mwaikambo , "Theodore Ts'o" , Randy Dunlap , Dave Jones , Chuck Wolber , Chris Wedgwood , Michael Krufky , Chuck Ebbert , Domenico Andreoli , torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Jeremy Fitzhardinge , Jeremy Fitzhardinge , Ingo Molnar Subject: xen: fix RMW when unmasking events Content-Disposition: inline; filename=xen-fix-rmw-when-unmasking-events.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org -stable review patch. If anyone has any objections, please let us know. --------------------- From: Jeremy Fitzhardinge upstream commit: 04c44a080d2f699a3042d4e743f7ad2ffae9d538 xen_irq_enable_direct and xen_sysexit were using "andw $0x00ff, XEN_vcpu_info_pending(vcpu)" to unmask events and test for pending ones in one instuction. Unfortunately, the pending flag must be modified with a locked operation since it can be set by another CPU, and the unlocked form of this operation was causing the pending flag to get lost, allowing the processor to return to usermode with pending events and ultimately deadlock. The simple fix would be to make it a locked operation, but that's rather costly and unnecessary. The fix here is to split the mask-clearing and pending-testing into two instructions; the interrupt window between them is of no concern because either way pending or new events will be processed. This should fix lingering bugs in using direct vcpu structure access too. Signed-off-by: Jeremy Fitzhardinge Signed-off-by: Ingo Molnar Signed-off-by: Chris Wright --- arch/x86/xen/enlighten.c | 2 +- arch/x86/xen/xen-asm.S | 9 +++++++-- 2 files changed, 8 insertions(+), 3 deletions(-) --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -95,7 +95,7 @@ struct shared_info *HYPERVISOR_shared_in * * 0: not available, 1: available */ -static int have_vcpu_info_placement = 0; +static int have_vcpu_info_placement = 1; static void __init xen_vcpu_setup(int cpu) { --- a/arch/x86/xen/xen-asm.S +++ b/arch/x86/xen/xen-asm.S @@ -33,12 +33,17 @@ events, then enter the hypervisor to get them handled. */ ENTRY(xen_irq_enable_direct) - /* Clear mask and test pending */ - andw $0x00ff, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_pending + /* Unmask events */ + movb $0, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_mask + /* Preempt here doesn't matter because that will deal with any pending interrupts. The pending check may end up being run on the wrong CPU, but that doesn't hurt. */ + + /* Test for pending */ + testb $0xff, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_pending jz 1f + 2: call check_events 1: ENDPATCH(xen_irq_enable_direct) --