Re: [PATCH v4 2/2] PCI/P2PDMA: Allow P2PDMA on Intel Xeon server CPUs

[sashiko-bot@kernel.org]

> Peer-to-Peer DMA (P2PDMA) between two devices requires either a shared
> upstream bridge or a host bridge matching pci_p2pdma_whitelist[]. In
> VMware guests, passthrough devices appear directly on virtual root
> buses without host bridge devices. In Hyper-V guests, each passthrough
> device appears in a PCI domain of its own without a host bridge
> device. Consequently, P2PDMA checks evaluate endpoint Device IDs
> against the host bridge whitelist, causing P2PDMA requests to fail
> regardless of host support.
> 
> This affects discrete devices such as GPUs, NICs and NVMe drives.
> 
> Add an explicit list of the Intel Xeon server generations from
> Skylake-SP to Diamond Rapids to cpu_supports_p2pdma(). These are the
> CPUs whose host bridges are in pci_p2pdma_whitelist[] without
> restrictions. AMD Zen and newer are already covered by
> cpu_supports_p2pdma(), so only Intel entries are needed.
> 
> Tested with the Intel Level Zero P2P benchmark (ze_peer) on Arc Pro B60
> cards in a Linux guest on VMware ESXi 9.0 (Emerald Rapids host).
> 
> Signed-off-by: Pavel Popov <pavel.e.popov@intel.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261020173736.81755-1-pavel.e.popov@intel.com?part=2