linux-kernel - Re: [Xen-devel] [RFC PATCH 04/16] x86/xen: hypercall support for xenhost

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Date:   Wed, 12 Jun 2019 22:15:44 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Ankur Arora <ankur.a.arora@...cle.com>,
        <linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>
CC:     <jgross@...e.com>, <sstabellini@...nel.org>,
        <konrad.wilk@...cle.com>, <pbonzini@...hat.com>,
        <boris.ostrovsky@...cle.com>, <joao.m.martins@...cle.com>
Subject: Re: [Xen-devel] [RFC PATCH 04/16] x86/xen: hypercall support for
 xenhost_t

On 09/05/2019 18:25, Ankur Arora wrote:
> Allow for different hypercall implementations for different xenhost types.
> Nested xenhost, which has two underlying xenhosts, can use both
> simultaneously.
>
> The hypercall macros (HYPERVISOR_*) implicitly use the default xenhost.x
> A new macro (hypervisor_*) takes xenhost_t * as a parameter and does the
> right thing.
>
> TODO:
>   - Multicalls for now assume the default xenhost
>   - xen_hypercall_* symbols are only generated for the default xenhost.
>
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>

Again, what is the hypervisor nesting and/or guest layout here?

I can't think of any case where a single piece of software can
legitimately have two hypercall pages, because if it has one working
one, it is by definition a guest, and therefore not privileged enough to
use the outer one.

~Andrew