Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754629AbZJ1Pfy (ORCPT ); Wed, 28 Oct 2009 11:35:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754592AbZJ1Pfy (ORCPT ); Wed, 28 Oct 2009 11:35:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36101 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754505AbZJ1Pfx (ORCPT ); Wed, 28 Oct 2009 11:35:53 -0400 From: Chris Lalancette To: mingo@elte.hu Cc: x86@kernel.org, mingo@redhat.com, kvm@vger.kernel.org, pbonzini@redhat.com, linux-kernel@vger.kernel.org, Chris Lalancette Subject: [PATCH] x86: Make sure get_user_desc() doesn't sign extend. Date: Wed, 28 Oct 2009 16:35:27 +0100 Message-Id: <1256744127-9056-1-git-send-email-clalance@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1586 Lines: 39 The current implementation of get_user_desc() sign extends the return value because of integer promotion rules. For the most part, this doesn't matter, because the top bit of base2 is usually 0. If, however, that bit is 1, then the entire value will be 0xffff... which is probably not what the caller intended. This patch casts the entire thing to unsigned before returning, which generates almost the same assembly as the current code but replaces the final "cltq" (sign extend) with a "mov %eax %eax" (zero-extend). This fixes booting certain guests under KVM. (2nd resend, since no response to the last two submissions) Signed-off-by: Chris Lalancette --- arch/x86/include/asm/desc.h | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h index e8de2f6..617bd56 100644 --- a/arch/x86/include/asm/desc.h +++ b/arch/x86/include/asm/desc.h @@ -288,7 +288,7 @@ static inline void load_LDT(mm_context_t *pc) static inline unsigned long get_desc_base(const struct desc_struct *desc) { - return desc->base0 | ((desc->base1) << 16) | ((desc->base2) << 24); + return (unsigned)(desc->base0 | ((desc->base1) << 16) | ((desc->base2) << 24)); } static inline void set_desc_base(struct desc_struct *desc, unsigned long base) -- 1.6.0.6 -- 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/