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

To:	"Tian, Kevin" <kevin.tian@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH] Clear VMCS if reusing after vcpu reset
From:	Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date:	Mon, 30 Apr 2007 08:12:20 +0100
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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).

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.

 -- Keir

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