RE: [Xen-devel] [PATCH] Clear VMCS if reusing after vcpu reset

To:	"Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject:	RE: [Xen-devel] [PATCH] Clear VMCS if reusing after vcpu reset
From:	"Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date:	Mon, 30 Apr 2007 15:19:10 +0800
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Thread-topic:	[Xen-devel] [PATCH] Clear VMCS if reusing after vcpu reset

>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
>Sent: 2007年4月30日 15:12
>
>On 30/4/07 07:09, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>
>> Clear whole page when VMCS is reused due to cpu hotplug.
>> construct_vmcs doesn't take care of all fields and some stale
>> content may make hardware unhappy.
>
>You almost certainly need to vmx_clear_vmcs() before you zap it, as
>there's
>no reason it might not be active on some CPU when vmx_create_vmcs()
>is
>called (domain_pause() does not deactivate VMCSs).

You're exactly right. :-)

>
>Furthermore, this need to zap the page a second time is worrying. We
>only
>modify architectural state in the VMCS in a well-defined way. That
>shouldn't
>upset the hardware. Is this actually an indication that there is some
>architectural state that we are forgetting to re-initialise? If so then
>that's the bug which should be fixed.
>

Does construct_vmcs need to explicitly care all fields if hardware 
just expects a zero there which can be satisfied by memset()? Anyway, 
I'll take a deeper look to check which unexpected fields are with stale 
content before reset.

Thanks,
Kevin

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