linux-kernel - Re: [RFC PATCH 07/16] x86/xen: make vcpu_info part of xenhost

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Date:   Sun, 16 Jun 2019 23:28:39 -0700
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Cc:     pbonzini@...hat.com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com, sstabellini@...nel.org,
        joao.m.martins@...cle.com
Subject: Re: [RFC PATCH 07/16] x86/xen: make vcpu_info part of xenhost_t

On 2019-06-14 4:53 a.m., Juergen Gross wrote:
> On 09.05.19 19:25, Ankur Arora wrote:
>> Abstract out xen_vcpu_id probing via (*probe_vcpu_id)(). Once that is
>> availab,e the vcpu_info registration happens via the VCPUOP hypercall.
>>
>> Note that for the nested case, there are two vcpu_ids, and two vcpu_info
>> areas, one each for the default xenhost and the remote xenhost.
>> The vcpu_info is used via pv_irq_ops, and evtchn signaling.
>>
>> The other VCPUOP hypercalls are used for management (and scheduling)
>> which is expected to be done purely in the default hypervisor.
>> However, scheduling of L1-guest does imply L0-Xen-vcpu_info switching,
>> which might mean that the remote hypervisor needs some visibility
>> into related events/hypercalls in the default hypervisor.
> 
> Another candidate for dropping due to layering violation, I guess.
Yeah, a more narrowly tailored interface, where perhaps the L1-Xen
maps events for L0-Xen makes sense.
Also, just realized that given that L0-Xen has no control over
scheduling of L1-Xen's guests (some of which it might want to
send events to), it makes sense for L1-Xen to have some state
for guest evtchns which pertain to L0-Xen.


Ankur

> 
> 
> Juergen