linux-kernel - KVM PV (was: Re: [PATCH v2 2/2] x86/lguest: remove lguest support)

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Message-ID: <CAJhGHyBY-ne6YeX=tT9BHbRx9bX_rmaBmFLLKPzCmrpmO9Z6Dg@mail.gmail.com>
Date:   Fri, 29 Sep 2017 23:47:21 +0800
From:   Lai Jiangshan <jiangshanlai+lkml@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org
Cc:     xen-devel@...ts.xenproject.org, x86@...nel.org,
        lguest@...ts.ozlabs.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        rusty@...tcorp.com.au, Juergen Gross <jgross@...e.com>
Subject: KVM PV (was: Re: [PATCH v2 2/2] x86/lguest: remove lguest support)

Hello, all

An interesting (at least to me) thinking came up to me when I found
that the lguest was removed. But I don't have enough knowledge
to find out the answer nor energy to implement it in some time.

Is it possible to implement kvm-pv which allows kvm to run on
the boxes without hardware virtualization support, so that
qemu/kvm can be used on clouds such as aws, azure?

Without hardware virtualization support, the host kvm-pv module and
the guest linux kernel need to cooperate in some ways. And some kvm
facilities can help. For instance, the existing shadow-paging, which
was not introduced when lguest had been added to kernel, could be
reused to help on mmu virtualization. For guest kernel/userspace
separation in x86_64, the intel cpu's segment registers can help too.
(or use a new set of page-table for the guest kernel on amd64).

The thought is quite shallow, but I hope this email brings some
inspirations rather than annoyance. And I'm sorry if the later things
would happen.

Thanks,
Lai.

On Thu, Aug 17, 2017 at 1:31 AM, Juergen Gross <jgross@...e.com> wrote:
> Lguest seems to be rather unused these days. It has seen only patches
> ensuring it still builds the last two years and its official state is
> "Odd Fixes".
>
> Nuke it in order to be able to clean up the paravirt code.