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Roger Pau Monne
024e7131be
The HVM pirq feature allows routing interrupts from both physical and emulated devices over event channels, this was done a performance improvement. However its usage is fully undocumented, and the only reference implementation is in Linux. It defeats the purpose of local APIC hardware virtualization, because when using it interrupts avoid the usage of the local APIC altogether. It has also been reported to not work properly with certain devices, at least when using some AMD GPUs Linux attempts to route interrupts over event channels, but Xen doesn't correctly detect such routing, which leads to the hypervisor complaining with: (XEN) d15v0: Unsupported MSI delivery mode 7 for Dom15 When MSIs are attempted to be routed over event channels the entry delivery mode is set to ExtINT, but Xen doesn't detect such routing and attempts to inject the interrupt following the native MSI path, and the ExtINT delivery mode is not supported. Disable HVM PIRQs by default and provide a per-domain option in xl.cfg to enable such feature. Also for backwards compatibility keep the feature enabled for any resumed domains that don't have an explicit selection. Note that the only user of the feature (Linux) is also able to handle native interrupts fine, as the feature was already not used if Xen reported local APIC hardware virtualization active. Link: https://github.com/QubesOS/qubes-issues/issues/7971 Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> Reviewed-by: Anthony PERARD <anthony.perard@citrix.com> Acked-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
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