Re: [PATCH RFC v2 0/2] arm: enable MTE for QEMU + kvm

[Peter Maydell]

On Mon, 11 Jul 2022 at 14:24, Dr. David Alan Gilbert
<dgilbert@redhat.com> wrote:
> But, ignoring postcopy for a minute, with KVM how do different types of
> backing memory work - e.g. if I back a region of guest memory with
> /dev/shm/something or a hugepage equivalent, where does the MTE memory
> come from, and how do you set it?

Generally in an MTE system anything that's "plain old RAM" is expected
to support tags. (The architecture manual calls this "conventional
memory". This isn't quite the same as "anything that looks RAM-like",
e.g. the graphics card framebuffer doesn't have to support tags!)

One plausible implementation is that the firmware and memory controller
are in cahoots and arrange that the appropriate fraction of the DRAM is
reserved for holding tags (and inaccessible as normal RAM even by the OS);
but where the tags are stored is entirely impdef and an implementation
could choose to put the tags in their own entirely separate storage if
it liked. The only way to access the tag storage is via the instructions
for getting and setting tags.

-- PMM