netdev - Re: [RFC 2/2] Set steering-tag directly for PCIe P2P memory access

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Message-ID: <20260113164923.GQ745888@ziepe.ca>
Date: Tue, 13 Jan 2026 12:49:23 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Zhiping Zhang <zhipingz@...a.com>
Cc: 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>
Subject: Re: [RFC 2/2] Set steering-tag directly for PCIe P2P memory access

On Mon, Jan 12, 2026 at 11:43:13PM -0800, Zhiping Zhang wrote:
> Got it, thanks for pointing out the security concern! To address this, I
> propose that we still pass the TPH value when allocating the dmah, but we add
> a verification callback in the reg_mr_dmabuf flow to the dmabuf exporter. This
> callback will ensure that the TPH value is correctly linked to the exporting
> device’s MMIO, and only the exporter can authorize the TPH/tag association.

That still sounds messy because we have to protect CPU memory.

I think you should not use dmah possibly and make it so the dmabuf
entirely supplies the TPH value.

Jason