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>
As a schema design comment. IIUC, the MMIO size we're configuring
is conceptually a characteristic associated with the PCI(e) host
and the memory layout it defines for PCI(e) devices to use.
Checking through our schema I find we already have support
for
<controller type='pci' index='0' model='pci-root'>
<pcihole64 unit='KiB'>1048576</pcihole64>
</controller>
this makes me think that we should model this new attribute
in a similar way, eg so we can support:
<controller type='pci' index='0' model='pci-root'>
<pcihole64 unit='KiB'>1048576</pcihole64>
<pcimmio64 unit='TiB'>2</pcimmio64>
</controller>
(pci-root or pcie-root are interchangable).
This 'pcimmio64' value can then be mapped to whatever hypervisor
or architecture specific setting is appropriate, avoiding exposing
the QEMU arm 'highmem-mmio-size' naming convention.
With regards,
Daniel
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