Hello Tushar, On Fri, 8 May 2026, at 20:37, Tushar Dave via groups.io wrote: > This RFC introduces a mechanism to specify Guest Physical Addresses > (GPAs) for PCI BARs, allowing explicit placement of guest MMIO BAR > addresses to match host physical addresses for assigned devices. > > On some platforms, P2P DMA is performed between devices within the same > IOMMU group. The PCI fabric ACS is configured to permit direct P2P > without going through the host bridge in order to achieve the required > performance. > > To support this multi-device IOMMU group P2P scenario in virtualization, > the VM may need to use the same MMIO BAR addresses as the host physical > address layout. >
Did you consider implementing this using Enhanced Allocation (EA)? If so, could you explain why it is not suitable here? Also, I think I understand what the intent is here, but could you describe the topology in a bit more detail? These are assigned physical PCIe endpoints behind an emulated host bridge, right? And the BAR needs to reside at an a priori fixed address so that another PCIe endpoint behind the same emulated host bridge can DMA straight into it? Doing PCIe enumeration at yet another level is not a feasible approach imo, having UEFI and Linux play nice together is already a bit of a challenge. Is there any way this could be handled by having special rules for inbound translation in the host bridge driver/implementation? -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#121927): https://edk2.groups.io/g/devel/message/121927 Mute This Topic: https://groups.io/mt/119221703/21656 Group Owner: [email protected] Unsubscribe: https://edk2.groups.io/g/devel/unsub [[email protected]] -=-=-=-=-=-=-=-=-=-=-=-
