ubuntu-mini-iso: Failed to find /dev/pmem0, debug shell

[Norbert]

Steps to reproduce:
1. Download latest ubuntu-mini-iso from https://cdimage.ubuntu.com/ubuntu-mini-iso/daily-live/current/noble-mini-iso-amd64.iso
2. Create virtual 32 Gb hard disk using

   fallocate -l32g 32g.raw

3. Launch QEMU VM with allocated 4 Gb of RAM

   kvm -cdrom ~/Downloads/noble-mini-iso-amd64.iso -drive file=32g.raw,format=raw -m 4096

4. Wait it to boot, select "Ubuntu Server 22.04.4 LTS (Jammy Jellyfish)" system to install.

Expected results:
* ubuntu-mini-iso is usable as it was in 20.04 LTS from http://archive.ubuntu.com/ubuntu/dists/focal/main/installer-amd64/current/legacy-images/netboot/mini.iso

Actual results:
* ubuntu-mini-iso is not usable and really useless - shows the following text in the QEMU terminal:

```
available memory insufficient
requested 2008MiB
available 1024MiB
failed to determine size reservation for memmap, debug shell
```

Additional notes: it seems that Ubuntu has turned into wrong direction, users of mini.iso should and will switch to Debian.

[Norbert (nrbrtx)]

It also fails with 32768 megabytes of RAM - shows different error:

```
Failed to find /dev/pmem0, debug shell
```

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Heinrich Schuchardt (xypron)]

ubuntu-mini-iso is used to download a installer image into a RAM disk and to use this installer image for the actual installation. Of course you need enough RAM for the installer image. Of course this cannot work if the RAM is smaller than the sum of both images.

I saw the same error 'Failed to find /dev/pmem0, debug shell' with

qemu-system-x86_64 \
-M q35,smm=on,accel=kvm \
-smp 4 \
-gdb tcp::1234 \
-serial mon:stdio \
-device virtio-gpu-pci \
-full-screen \
-global driver=cfi.pflash01,property=secure,value=on \
-drive if=pflash,format=raw,unit=0,file=/usr/share/OVMF/OVMF_CODE_4M.fd,readonly=on \
-drive if=pflash,format=raw,unit=1,file=OVMF_VARS_4M.fd \
-cdrom /tmp/noble-mini-iso-amd64.iso \
-drive file=32g.raw,format=raw \
-m 8192