From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757940AbXFNXNk (ORCPT ); Thu, 14 Jun 2007 19:13:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753110AbXFNXNd (ORCPT ); Thu, 14 Jun 2007 19:13:33 -0400 Received: from ik-out-1112.google.com ([66.249.90.183]:18308 "EHLO ik-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752904AbXFNXNc (ORCPT ); Thu, 14 Jun 2007 19:13:32 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:date:from:to:subject:message-id:mail-followup-to:references:mime-version:content-type:content-disposition:in-reply-to:user-agent; b=JY0qn8w6P1enA6+ERzcMuMvnvVHnNr9zJaoZYq6azbUT7bgKtmeaWfcrLKCmx/0T/2CmFCn26jkOSNLPxb8nHdZVpzHDNSayDYaqeB/7O13Yg5+NDNt4OnKIfea6WEQHGap/1tLqriVbfuIHMpJhtimgAiDk8rltLIpaWfEJ30Y= Date: Fri, 15 Jun 2007 01:13:59 +0200 From: Luca Tettamanti To: Avi Kivity , kvm-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [kvm-devel] [BUG] Oops with KVM-27 Message-ID: <20070614231359.GA5705@dreamland.darkstar.lan> Mail-Followup-To: Avi Kivity , kvm-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org References: <46651069.5040003@qumranet.com> <68676e00706071216i4bd051c5hb1c114f3c13ab97f@mail.gmail.com> <466BED18.5040708@qumranet.com> <68676e00706101354n5fe7e1a9y12cb690cae2924e3@mail.gmail.com> <466CFD6D.2080201@qumranet.com> <20070612175246.GA5864@dreamland.darkstar.lan> <466FB1ED.3090905@qumranet.com> <20070613204948.GA14710@dreamland.darkstar.lan> <4670FBB5.70707@qumranet.com> <20070614225324.GA4088@dreamland.darkstar.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070614225324.GA4088@dreamland.darkstar.lan> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Il Fri, Jun 15, 2007 at 12:53:24AM +0200, Luca Tettamanti ha scritto: > Il Thu, Jun 14, 2007 at 11:26:29AM +0300, Avi Kivity ha scritto: > > Luca Tettamanti wrote: > > >With GOOD_APIC apic_read_around is a nop, while apic_write_around is a > > >normal write. With !GOOD_APIC apic_write_around writes to the APIC reg > > >using xchg. With !GOOD_APIC and this patch: > > > > > >--- include/asm-i386/apic.h~ 2007-04-26 05:08:32.000000000 +0200 > > >+++ include/asm-i386/apic.h 2007-06-13 22:35:00.000000000 +0200 > > >@@ -56,7 +56,8 @@ > > > static __inline fastcall void native_apic_write_atomic(unsigned long reg, > > > unsigned long v) > > > { > > >- xchg((volatile unsigned long *)(APIC_BASE+reg), v); > > >+// xchg((volatile unsigned long *)(APIC_BASE+reg), v); > > >+ *((volatile unsigned long *)(APIC_BASE+reg)) = v; > > > } > > > > > > static __inline fastcall unsigned long native_apic_read(unsigned long reg) > > > > > >The kernel boots fine. > > > > > > > Looking at the xchg emulation code, it seems fine, but clearly it > > isn't. > > Btw, I've put a printk in x86_emulate.c, where it prepares the operands > for the xchg operations: all the write_atomic are hitting this point, > so the write is lost somewhere in cmpxchg_emulated->write_emulated. Got it! The emulator skips the writeback if the old value is unchanged, so the apic doesn't see the write. Forcing the writeback: - if ((d & Mov) || (dst.orig_val != dst.val)) { - if ((d & Mov) || (dst.orig_val != dst.val) || isxchg) { seems to fix the issue :D I'm not sure that fix is correct though. This is the patch I'm using: --- a/kernel/x86_emulate.c 2007-06-03 10:31:15.000000000 +0200 +++ b/kernel/x86_emulate.c 2007-06-15 01:12:12.000000000 +0200 @@ -486,6 +486,7 @@ unsigned long _regs[NR_VCPU_REGS]; unsigned long _eip = ctxt->vcpu->rip, _eflags = ctxt->eflags; unsigned long modrm_val = 0; + int isxchg = 0; memcpy(_regs, ctxt->vcpu->regs, sizeof _regs); @@ -912,6 +913,7 @@ break; case 0x86 ... 0x87: /* xchg */ /* Write back the register source. */ + isxchg = 1; switch (dst.bytes) { case 1: *(u8 *) src.ptr = (u8) dst.val; @@ -1056,7 +1058,7 @@ } writeback: - if ((d & Mov) || (dst.orig_val != dst.val)) { + if ((d & Mov) || (dst.orig_val != dst.val) || isxchg) { switch (dst.type) { case OP_REG: /* The 4-byte case *is* correct: in 64-bit mode we zero-extend. */ Luca -- "Su cio` di cui non si puo` parlare e` bene tacere". Ludwig Wittgenstein