linux-kernel - Re: [RFC PATCH 06/16] x86/xen: add shared_info support to xenhost

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Message-ID: <71126f1a-ad50-cf4e-2cc8-5a778a7ecbb4@oracle.com>
Date:   Fri, 7 Jun 2019 22:01:37 -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 06/16] x86/xen: add shared_info support to xenhost_t

On 2019-06-07 8:08 a.m., Juergen Gross wrote:
> On 09.05.19 19:25, Ankur Arora wrote:
>> HYPERVISOR_shared_info is used for irq/evtchn communication between the
>> guest and the host. Abstract out the setup/reset in xenhost_t such that
>> nested configurations can use both xenhosts simultaneously.
> 
> I have mixed feelings about this patch. Most of the shared_info stuff we
> don't need for the nested case. In the end only the event channels might
> be interesting, but we obviously want them not for all vcpus of the L1
> hypervisor, but for those of the current guest.
Agreed about the mixed feelings part. shared_info does feel far too
heavy to drag along just for the event-channel state.
Infact, on thinking a bit more, a better abstraction for nested
event-channels would have been as an extension to the primary
xenhost's event-channel bits.
(The nested upcalls also go via the primary xenhost in patch-8.)

Ankur

> 
> So I think just drop that patch for now. We can dig it out later in case > nesting wants it again.
> 
> 
> Juergen