Re: Unmapping KVM Guest Memory from Host Kernel

Fuad Tabba
2024-03-11T09:27:13Z

Hi,

On Fri, Mar 8, 2024 at 9:05 PM Manwaring, Derek <derekmn@amazon.com> wrote:
>
> On 2024-03-08 at 10:46-0700, David Woodhouse wrote:
> > On Fri, 2024-03-08 at 09:35 -0800, David Matlack wrote:
> > > I think what James is looking for (and what we are also interested
> > > in), is _eliminating_ the ability to access guest memory from the
> > > direct map entirely. And in general, eliminate the ability to access
> > > guest memory in as many ways as possible.
> >
> > Well, pKVM does that...
>
> Yes we've been looking at pKVM and it accomplishes a lot of what we're trying
> to do. Our initial inclination is that we want to stick with VHE for the lower
> overhead. We also want flexibility across server parts, so we would need to
> get pKVM working on Intel & AMD if we went this route.
>
> Certainly there are advantages of pKVM on the perf side like the in-place
> memory sharing rather than copying as well as on the security side by simply
> reducing the TCB. I'd be interested to hear others' thoughts on pKVM vs
> memfd_secret or general ASI.

The work we've done for pKVM is still an RFC [*], but there is nothing
in it that limits it to nVHE (at least not intentionally). It should
work with VHE and hVHE as well. On respinning the patch series [*], we
plan on adding support for normal VMs to use guest_memfd() as well in
arm64, mainly for testing, and to make it easier for others to base
their work on it.

Cheers,
/fuad

[*] https://lore.kernel.org/all/20240222161047.402609-1-tabba@google.com
>
> Derek
>