xen-devel

[Top] [All Lists]

Re: [Xen-devel] [Patch] cmpxchg emulation returns wrong ZF

from [Jan Beulich]

[Permanent Link][Original]

To:	"Juergen Gross" <juergen.gross@xxxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] [Patch] cmpxchg emulation returns wrong ZF
From:	"Jan Beulich" <JBeulich@xxxxxxxxxx>
Date:	Thu, 06 Aug 2009 09:01:48 +0100
Cc:	"xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date:	Thu, 06 Aug 2009 01:02:20 -0700
Envelope-to:	www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to:	<4A7A7CEB.9080702@xxxxxxxxxxxxxx>
List-help:	<mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id:	Xen developer discussion <xen-devel.lists.xensource.com>
List-post:	<mailto:xen-devel@lists.xensource.com>
List-subscribe:	<http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe:	<http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References:	<4A7A7CEB.9080702@xxxxxxxxxxxxxx>
Sender:	xen-devel-bounces@xxxxxxxxxxxxxxxxxxx

>>> Juergen Gross <juergen.gross@xxxxxxxxxxxxxx> 06.08.09 08:49 >>>
>Hi,
>
>attached patch corrects a bug in cmpxchg emulation in the hypervisor.
>
>BS2000 running as HVM-domain on 4 vcpus (no HAP) hit an error due to this bug
>after several days.

Why don't you just clear ZF in that case? I think it is intentional that the
code doesn't loop inside the hypervisor, since that loop is non-preemptible
(whereas returning to the guest and re-issuing the instruction is).

Further, I'm not really clear why that change is necessary at all: In the
code prior to the patch, register state is not being updated if
ops->cmpxchg() failed, and hence the old value of ZF is simply being
retained - which is the correct thing to do when intending to re-start
the instruction.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel

[More with this subject...]

<Prev in Thread]	Current Thread	[Next in Thread>
[Xen-devel] [Patch] cmpxchg emulation returns wrong ZF, Juergen Gross Re: [Xen-devel] [Patch] cmpxchg emulation returns wrong ZF, Jan Beulich <= Re: [Xen-devel] [Patch] cmpxchg emulation returns wrong ZF, Juergen Gross Re: [Xen-devel] [Patch] cmpxchg emulation returns wrong ZF, Keir Fraser

Previous by Date:	Re: [Xen-devel] [pvops-dom0] Adding MCA logging support in pv_ops, Christoph Egger
Next by Date:	Re: [Xen-devel] [Patch] cmpxchg emulation returns wrong ZF, Juergen Gross
Previous by Thread:	[Xen-devel] [Patch] cmpxchg emulation returns wrong ZF, Juergen Gross
Next by Thread:	Re: [Xen-devel] [Patch] cmpxchg emulation returns wrong ZF, Juergen Gross
Indexes:	[Date] [Thread] [Top] [All Lists]