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Date: Fri, 9 Oct 2026 11:58:33 -0500
From: Bjorn Helgaas <helgaas@kernel.org>
To: Pavel Popov <pavel.e.popov@intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	Logan Gunthorpe <logang@deltatee.com>,
	Jim Chow <jim.chow@broadcom.com>,
	Radu Rugina <radu.rugina@broadcom.com>,
	Alexey Makhalov <alexey.makhalov@broadcom.com>,
	Wei Liu <wei.liu@kernel.org>, Michael Kelley <mhklinux@outlook.com>,
	Lukas Wunner <lukas@wunner.de>, Leon Romanovsky <leonro@nvidia.com>,
	Nathan Ciobanu <nathan.d.ciobanu@linux.intel.com>,
	bcm-kernel-feedback-list@broadcom.com,
	virtualization@lists.linux.dev, linux-hyperv@vger.kernel.org,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2] PCI/P2PDMA: Allow P2PDMA in VMware and Hyper-V
 guests on Intel hosts
Message-ID: <20261009165833.GA991924@bhelgaas>
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In-Reply-To: <20261009154034.82321-1-pavel.e.popov@intel.com>

On Fri, Oct 09, 2026 at 08:40:32AM -0700, Pavel Popov wrote:
> VMware and Hyper-V expose passthrough devices to guest VMs without an
> explicit host bridge device. Consequently, host_bridge_whitelist()
> cannot automatically identify the underlying host bridge structure,
> causing Peer-to-Peer DMA (P2PDMA) requests to be rejected unless the
> device IDs are explicitly listed in pci_p2pdma_whitelist[]. To enable
> P2PDMA support in virtualized environments on Intel hosts, this series
> introduces hypervisor_supports_p2pdma().
> 
> Although alternative P2PDMA mechanisms are in development [1], their
> adoption timeline in hypervisors remains uncertain. This solution
> addresses the immediate need to support both new and existing
> hypervisor deployments.
> 
> The patches are organized by hypervisor for clarity. While the primary
> focus is VMware, a corresponding Hyper-V patch addresses the same
> pattern and is included for maintainer consideration.
> 
> [1] https://lore.kernel.org/r/20260812-hmat-p2p-v1-0-75ac41380585@nvidia.com
> 
> Pavel Popov (2):
>   PCI/P2PDMA: Allow P2PDMA in VMware guests on Intel hosts
>   PCI/P2PDMA: Allow P2PDMA in Hyper-V guests on Intel hosts
> 
>  drivers/pci/p2pdma.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)

Applied with the #ifdef tweak Logan suggested to pci/p2pdma for v7.4,
thanks!

FWIW, it's better if responses like Jim's Reviewed-by actually appear
on the mailing list.  I don't see anything in lore, so I assume it
must have been private review.