Re: [RFC PATCH 00/39] 1G page support for guest_memfd

[Vishal Annapurve]

On Fri, Sep 13, 2024 at 6:08 PM Du, Fan <fan.du@xxxxxxxxx> wrote:
>
> ...
> >
> > Hello,
> >
> > This patchset is our exploration of how to support 1G pages in guest_memfd,
> > and
> > how the pages will be used in Confidential VMs.
> >
> > The patchset covers:
> >
> > + How to get 1G pages
> > + Allowing mmap() of guest_memfd to userspace so that both private and
> > shared
>
> Hi Ackerley
>
> Thanks for posting new version :)
>
> W.r.t above description and below patch snippet from Patch 26-29,
> Does this new design aim to backup shared and private GPA with a single
> Hugetlb spool which equal VM instance total memory?

Yes.
>
> By my understanding, before this new changes, shared memfd and gmem fd
> has dedicate hugetlb pool, that's two copy/reservation of hugetlb spool.

Selftests attached to this series use single gmem fd to back guest memory.

>
> Does Qemu require new changes as well? I'd like to have a test of this series
> if you can share Qemu branch?
>

We are going to discuss this RFC series and related issues at LPC.
Once the next steps are finalized, the plan will be to send out an
improved version. You can use/modify the selftests that are part of
this series to test this feature with software protected VMs for now.

Qemu will require changes for this feature on top of already floated
gmem integration series [1] that adds software protected VM support to
Qemu. If you are interested in testing this feature with TDX VMs then
it needs multiple series to set up the right test environment
(including [2]). We haven't considered posting Qemu patches and it
will be a while before we can get to it.

[1] https://patchew.org/QEMU/20230914035117.3285885-1-xiaoyao.li@xxxxxxxxx/
[2] https://patchwork.kernel.org/project/kvm/cover/20231115071519.2864957-1-xiaoyao.li@xxxxxxxxx/