[libvirt] Re: [PATCH] Add huge page support to libvirt, v2..
On Mon, 2009-07-27 at 22:55 +0100, Daniel P. Berrange wrote:
On Thu, Jul 23, 2009 at 09:00:18PM -0400, john cooper wrote:
> I've incorporated feedback received on the
> prior version into the patch below.
>
> The host mount point for hugetlbfs is queried by
> default from /proc/mounts unless overridden in
> qemu.conf via:
>
> hugepage_mount = "<path_to_mount_point>"
>
> This should make the concern of establishing
> a mount point path convention a non-issue for
> the general case while still allowing the same
> to be deterministically set if needed.
In light of what Chris said about extended attribute support
for SELinux I think we, sadly, have no choice by to mount
a new instance of hugetlbfs per VM, labelled with the context
of that VM.
I haven't played with hugetlbfs much, so let me make sure I understand
the issue:
-) With --mempath, qemu creates a file under the supplied directory
and mmap()s it, using the mapped region for guest memory
-) Because the directory is under hugetlbfs, that memory is huge page
backed
-) Guest memory can be read by reading this file
-) The file is owned by the uid of the qemu process, so any other
processes with that uid can access guest memory
-) If we could label the file, we could use policy to prevent qemu
processes from accessing each other's files
-) We can't, so the alternative is to use a separate hugetlbfs mount
for each guest, each with a different label - each mount will only
contain the file for that guest, and only be accessible by that
guest
Cheers,
Mark.