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SubjectRe: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future CPUs
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On 20/02/2018 15:59, Van De Ven, Arjan wrote:
>
>>> I meant software wise. You're not going to live migrate from xen to
>>> kvm or backwards. or between very radically different versions of the
>>> kvm stack.
>>
>> Forwards migration to a radically newer version certainly happens. So
>> when the source hypervisor was too old to tell the VM about IBRS_ALL,
>> for example, migration should work properly and the VM should perform
>> well on the destination hypervisor.
>
> that makes sense, compatibility in this direction can be done
> and is useful as you move a fleet of servers forward
>
>> Backwards migration to older hypervisors also happens sometimes, but in
>> general it creates more userspace than kernel issues.
>
> that direction is obviously harder

From KVM's point of view it's mostly a matter of having a complete ioctl
API right. I'm not that much worried by it.

Paolo

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