netdev - [RFC 0/2] Retrieve tph from dmabuf for PCIe P2P memory access

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Message-ID: <20260209175317.1713406-1-zhipingz@meta.com>
Date: Mon, 9 Feb 2026 09:53:10 -0800
From: Zhiping Zhang <zhipingz@...a.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
        Bjorn
 Helgaas <bhelgaas@...gle.com>, <linux-rdma@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <netdev@...r.kernel.org>,
        Keith Busch
	<kbusch@...nel.org>, Yochai Cohen <yochai@...dia.com>,
        Yishai Hadas
	<yishaih@...dia.com>
CC: Bjorn Helgaas <helgaas@...nel.org>, Zhiping Zhang <zhipingz@...a.com>
Subject: [RFC 0/2] Retrieve tph from dmabuf for PCIe P2P memory access

Currently, the steering tag can be used for a CPU on the motherboard; the
ACPI check is in place to query and obtain the supported tph settings. Here
we intend to use the tph info to improve RDMA NIC memory access on a vfio-based
accelerator device via PCIe peer-to-peer. When an applicantion register a
RDMA memory region with DMABUF for the RDMA NIC to access the device memory,
the tph associated with the memory region can be retrieved and used to set the
steering tag / process hint (ph). The tph contains additional instructions
or hints to the GPU or accelerator device for advanced memory operations,
such as, read cache selection.

Note this RFC is for the discussion on the direction and is not intended to be
a complete implementation. Once the direction is agreed on, we will work on the
implementation or a real patch set.

Signed-off-by: Zhiping Zhang <zhipingz@...a.com>

[RFC 1/2] Vfio: add callback to get tph info for dmabuf
[RFC 2/2] RMDA MLX5: get tph for p2p access when registering dmabuf