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Re: [PATCH v2 2/4] x86: Introduce MSR_UNHANDLED

  • To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
  • Date: Fri, 19 Feb 2021 09:56:32 -0500
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  • Delivery-date: Fri, 19 Feb 2021 14:56:51 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 2/18/21 5:51 AM, Roger Pau Monné wrote:
> On Wed, Jan 20, 2021 at 05:49:10PM -0500, Boris Ostrovsky wrote:
>> When toolstack updates MSR policy, this MSR offset (which is the last
>> index in the hypervisor MSR range) is used to indicate hypervisor
>> behavior when guest accesses an MSR which is not explicitly emulated.
> It's kind of weird to use an MSR to store this. I assume this is done
> for migration reasons?

Not really. It just seemed to me that MSR policy is the logical place to do 
that. Because it *is* a policy of how to deal with such accesses, isn't it?

> Isn't is possible to convey this data in the xl migration stream
> instead of having to pack it with MSRs?

I haven't looked at this but again --- the feature itself has nothing to do 
with migration. The fact that folding it into policy makes migration of this 
information "just work" is just a nice side benefit of this implementation.




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