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

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Message-ID: <4F8ECA4F.7070305@redhat.com>
Date:	Wed, 18 Apr 2012 17:06:07 +0300
From:	Avi Kivity <avi@...hat.com>
To:	"Nadav Har'El" <nyh@...h.technion.ac.il>
CC:	Anthony Liguori <anthony@...emonkey.ws>, kvm@...r.kernel.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] Export offsets of VMCS fields as note information
 for kdump

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.

-- 
error compiling committee.c: too many arguments to function

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