Speaker
Description
PCIe TPH enables cache steering for high-performance P2PDMA, RDMA and SDXI workloads. Today Linux only supports TPH operations within host kernel space; userspace/VFIO passthrough environments lack a standard interface to resolve and program steering tags.
I’ve posted a complete patch series adding native VFIO TPH support, aligned with community incremental security policy design. The series provides unified handling for CPU memory (via root port ACPI _DSM), dma-buf, zero-tag and literal raw ST sources, supporting cross-device P2P DMA scenarios. Three new VFIO_DEVICE_FEATURE ioctls cover feature opt-in, multi-source tag resolution and batch ST table programming.
Current upstream challenges include:
Automated selftest coverage without physical TPH hardware;
Lock granularity performance tradeoffs for batch ST programming;
Security boundary definition for cross-device dma-buf TPH metadata access.
The core uAPI and security logic are stable and targeted for v7.3 merge window in late August. Post-merge follow-up plans include extending QEMU to emulate TPH capabilities and implementing full guest passthrough support with VMM-managed _DSM emulation.
This session will briefly introduce the design, then focus on resolving the outstanding upstream challenges and aligning on VM passthrough roadmap.