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Re: [qemu-s390x] [PATCH 2/3] s390x/kvm: Handle bpb feature

From: Christian Borntraeger
Subject: Re: [qemu-s390x] [PATCH 2/3] s390x/kvm: Handle bpb feature
Date: Wed, 17 Jan 2018 15:44:39 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 01/17/2018 03:30 PM, David Hildenbrand wrote:
> On 17.01.2018 15:18, Christian Borntraeger wrote:
>> We need to handle the bpb control on reset and migration. Normally
>> stfle.82 is transparent (and the normal guest part works without
>> hypervisor activity). To prevent any issues we require full
>> host kernel support for this feature.
> Actually it is not transparent because we need hypervisor support to get
> VSIE running... or what am I missing? (or were you talking about bit 81?)

When you pass along the bit as a transparent bit (just enable it if the host
has it) it will work in nested guests. Its only that after reset or vsie you
have a short period of time where you work in a stale state.
Anyway we are aware that bit82 should have been a non-transparent bit, consider
it a quirk in the architecture. Thats why I handle this feature not in patch 3.

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