Re: [PATCH 0/4] Export offsets of VMCS fields as note information for kdump

[Avi Kivity <avi@redhat.com>]

On 04/18/2012 04:47 PM, Nadav Har'El wrote:
> On Wed, Apr 18, 2012, Avi Kivity wrote about "Re: [PATCH 0/4] Export offsets of VMCS fields as note information for kdump":
> > Right; they're also not required to be in memory at all - the processor
> > can cache them, even for VMCSs that are not active at this time. 
> > Running VMXOFF at panic time can fix that, but you have to broadcast it
> > to all processors, probably using NMI...
>
> I believe that a VMCLEAR ensures that the VMCS is written back to
> memory. KVM uses this fact when migrating a VMCS between two separate
> physical CPUs - it runs VMCLEAR on the old CPU, to write the VMCS to
> memory, and then VMPTRLD on the new CPU.
>
> So you don't need to VMXOFF, but do need to VMCLEAR. But there's still
> the complication that you mention - you need to do the VMCLEAR on the right
> processor...

VMCLEAR only clears one VMCS; several may be cached by a processor at
one time.  Presumably VMXOFF flushes everything.

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