On 2/25/26 08:48, Xiaotian Feng via Devel wrote:
This series refines libvirt's logic for large vCPU configurations (>255) on x86/q35 machine types. Historically, the threshold was tied to Intel's EIM capability, but the real requirement is x2APIC support for APIC IDs beyond 255. AMD platforms can satisfy this via xtsup on amd-iommu.
Summary of changes:
1. Fix virDomainIOMMUDefEquals to include pt and xtsup attributes for proper checks.
2. Correct error messages for passthrough (pt) and xtsup attributes to reflect their actual names instead of "dma translation".
3. Rename QEMU_MAX_VCPUS_WITHOUT_EIM to QEMU_MAX_VCPUS_WITHOUT_X2APIC and update validation logic to accept either: - intel-iommu with eim='on', or - amd-iommu with xtsup='on' for guests with more than 255 vCPUs. Error messages now mention x2APIC mode instead of extended interrupt mode.
4. Add QEMU_CAPS_AMD_IOMMU_XTSUP capability and enable xtsup by default for AMD IOMMU when a Q35 domain has >255 vCPUs, similar to Intel EIM auto-enable logic. Also ensure intremap is turned on when required.
This makes the behavior vendor-neutral and improves usability for AMD EPYC guests with large vCPU counts.
No ABI changes beyond stricter equality checks; this is a clarification and extension of existing logic.
Xiaotian Feng (4): conf: fix virDomainIOMMUDefEquals for amd_iommu conf: fix error log for passthrough and xtsup attributes conf: support >255 vcpu w/ amd-iommu xtsup qemu: Enable AMD IOMMU XTSUP by default
src/conf/domain_conf.c | 6 ++++-- src/qemu/qemu_capabilities.c | 2 ++ src/qemu/qemu_capabilities.h | 1 + src/qemu/qemu_postparse.c | 42 +++++++++++++++++++++++------------- src/qemu/qemu_validate.c | 11 +++++----- src/qemu/qemu_validate.h | 2 +- 6 files changed, 41 insertions(+), 23 deletions(-)
Reviewed-by: Michal Privoznik <mprivozn@redhat.com> and merged. Congratulations on your first libvirt contribution! Michal