Here's another stab at enabling QEMU on systems with pathologically
reduced IPA ranges such as the Apple M1 (previous version at [1]).
Eventually, we're able to run a KVM guest with more than just 3GB of
RAM on a system with a 36bit IPA space, and at most 123 vCPUs.

This also addresses some pathological QEMU behaviours, where the
highmem property is used as a flag allowing exposure of devices that
can't possibly fit in the PA space of the VM, resulting in a guest
failure.

In the end, we generalise the notion of PA space when exposing
individual devices in the expanded memory map, and treat highmem as
another flavour or PA space restriction.

This series does a few things:

- introduce new attributes to control the enabling of the highmem
  GICv3 redistributors and the highmem PCIe MMIO range

- correctly cap the PA range with highmem is off

- generalise the highmem behaviour to any PA range

- disable each highmem device region that doesn't fit in the PA range

- cleanup uses of highmem outside of virt_set_memmap()

This has been tested on an M1-based Mac-mini running Linux v5.16-rc6
with both KVM and TCG.

* From v3 [1]:

  - Introduced highmem_mmio as the MMIO pendant to highmem_ecam after
    Eric made it plain that I was misguided in using highmem_ecam to
    gate the MMIO region.

  - Fixed the way the top of RAM is enforced (using the device memory
    size, rounded up to the nearest GB). I long debated *not* using
    the rounded up version, but finally decided that it would be the
    least surprising, given that each slot is supposed to hold a full
    GB.

  - Now allowing some of the highmem devices to be individually
    enabled if they fit in the PA range. For example, a system with a
    39bit PA range and at most 255GB of RAM can use the highmem redist
    and PCIe ECAM ranges, but not the high PCIe range.

  - Dropped some of Andrew's RBs, as the code significantly changed.

[1] https://lore.kernel.org/r/20211227211642.994461-1-maz@kernel.org

Marc Zyngier (6):
  hw/arm/virt: Add a control for the the highmem PCIe MMIO
  hw/arm/virt: Add a control for the the highmem redistributors
  hw/arm/virt: Honor highmem setting when computing the memory map
  hw/arm/virt: Use the PA range to compute the memory map
  hw/arm/virt: Disable highmem devices that don't fit in the PA range
  hw/arm/virt: Drop superfluous checks against highmem

 hw/arm/virt-acpi-build.c | 10 ++---
 hw/arm/virt.c            | 87 +++++++++++++++++++++++++++++++++++-----
 include/hw/arm/virt.h    |  5 ++-
 3 files changed, 85 insertions(+), 17 deletions(-)

-- 
2.30.2