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

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Date:   Thu, 21 Feb 2019 08:57:17 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>,
        Joao Martins <joao.m.martins@...cle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        x86@...nel.org, Ankur Arora <ankur.a.arora@...cle.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Xen-devel] [PATCH RFC 00/39] x86/KVM: Xen HVM guest support

On 21/02/2019 00:39, Marek Marczykowski-Górecki wrote:
> On Wed, Feb 20, 2019 at 08:15:30PM +0000, 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).
> 
> Does it mean backends could be run in another guest, similarly as on
> real Xen? AFAIK virtio doesn't allow that as virtio backends need
> arbitrary write access to guest memory. But grant tables provide enough
> abstraction to do that safely.

As long as the grant table emulation in xen-shim isn't just a wrapper to
"normal" KVM guest memory access.

I guess the xen-shim implementation doesn't support the same kind of
guest memory isolation as Xen does?


Juergen