linux-kernel - Re: [kvm-devel] [BUG] Oops with KVM-27

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Message-ID: <20070614225324.GA4088@dreamland.darkstar.lan>
Date:	Fri, 15 Jun 2007 00:53:24 +0200
From:	Luca Tettamanti <kronos.it@...il.com>
To:	Avi Kivity <avi@...ranet.com>
Cc:	kvm-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [kvm-devel] [BUG] Oops with KVM-27

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.

Luca
-- 
Il dottore mi ha detto di smettere di fare cene intime per quattro.
A meno che non ci siamo altre tre persone.
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