Re: [PATCH RESEND 0/6] Add support for configuring PCI high memory MMIO size
On Fri, Apr 11, 2025 at 08:40:54AM -0700, Matthew R. Ochs via Devel wrote:
Resending: Series has been re-based over latest upstream.
This patch series adds support for configuring the PCI high memory MMIO
window size for aarch64 virt machine types. This feature has been merged
into the QEMU upstream master branch [1] and will be available in QEMU 10.0.
It allows users to configure the size of the high memory MMIO window above
4GB, which is particularly useful for systems with large amounts of PCI
memory requirements.
The feature is exposed through the domain XML as a new PCI feature:
<features>
<pci>
<highmem-mmio-size unit='G'>512</highmem-mmio-size>
</pci>
</features>
When enabled, this configures the size of the PCI high memory MMIO window
via QEMU's highmem-mmio-size machine property. The feature is only
available for aarch64 virt machine types and requires QEMU support.
This isn't my area of expertize, but could you give any more background
on why we need to /manually/ set such a property on Arm only ? Is there
something that prevents us making QEMU "do the right thing" ?
As a general rule these kind of obscure tunables are not very user
friendly. Since they are obscure, most mgmt apps developers are not
going to be aware of them, so may well not provide any way to set
them, and even if they can be set, it still requires someone or
something to remember to actually set it... which usually ends up
only happening /after/ the end user has complained their setup
is broken. Overall this leads to a poor user experience IME.
IOW, if there is any plausible way we can make QEMU work suitably
out of the box, that'd be preferrable to requiring a manually set
obscure tunable like this
This series depends on [2] and should be applied on top of those
patches.
For your convenience, this series is also available on Github [3].
[1] https://github.com/qemu/qemu/commit/f10104aeae3a17f181d5bb37b7fd7dad7fe86cba
[2]
https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/Z4...
[3] git fetch https://github.com/nvmochs/libvirt.git pci_highmem_mmio_size
Signed-off-by: Matthew R. Ochs <mochs(a)nvidia.com>
Matthew R. Ochs (6):
domain: Add PCI configuration feature infrastructure
schema: Add PCI configuration feature schema
conf: Add PCI configuration XML parsing and formatting
qemu: Add capability for PCI high memory MMIO size
qemu: Add command line support for PCI high memory MMIO size
tests: Add tests for machine PCI features
src/conf/domain_conf.c | 103 ++++++++++++++++++
src/conf/domain_conf.h | 6 +
src/conf/schemas/domaincommon.rng | 9 ++
src/qemu/qemu_capabilities.c | 2 +
src/qemu/qemu_capabilities.h | 1 +
src/qemu/qemu_command.c | 6 +
src/qemu/qemu_validate.c | 15 +++
.../caps_10.0.0_aarch64.replies | 10 ++
.../caps_10.0.0_aarch64.xml | 1 +
...rch64-virt-machine-pci.aarch64-latest.args | 31 ++++++
...arch64-virt-machine-pci.aarch64-latest.xml | 30 +++++
.../aarch64-virt-machine-pci.xml | 20 ++++
tests/qemuxmlconftest.c | 2 +
13 files changed, 236 insertions(+)
create mode 100644 tests/qemuxmlconfdata/aarch64-virt-machine-pci.aarch64-latest.args
create mode 100644 tests/qemuxmlconfdata/aarch64-virt-machine-pci.aarch64-latest.xml
create mode 100644 tests/qemuxmlconfdata/aarch64-virt-machine-pci.xml
--
2.46.0
With regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|