linux-kernel - Re: [PATCH RFC 00/39] x86/KVM: Xen HVM guest support

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Date:   Wed, 20 Feb 2019 22:09:00 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Joao Martins <joao.m.martins@...cle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Ankur Arora <ankur.a.arora@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH RFC 00/39] x86/KVM: Xen HVM guest support

On 20/02/19 21:15, Joao Martins wrote:
>  2. PV Driver support (patches 17 - 39)
> 
>  We start by redirecting hypercalls from the backend to routines
>  which emulate the behaviour that PV backends expect i.e. grant
>  table and interdomain events. Next, we add support for late
>  initialization of xenbus, followed by implementing
>  frontend/backend communication mechanisms (i.e. grant tables and
>  interdomain event channels). Finally, introduce xen-shim.ko,
>  which will setup a limited Xen environment. This uses the added
>  functionality of Xen specific shared memory (grant tables) and
>  notifications (event channels).

I am a bit worried by the last patches, they seem really brittle and
prone to breakage.  I don't know Xen well enough to understand if the
lack of support for GNTMAP_host_map is fixable, but if not, you have to
define a completely different hypercall.

Of course, tests are missing.  You should use the
tools/testing/selftests/kvm/ framework, and ideally each patch should
come with coverage for the newly-added code.

Thanks,

Paolo