Peer-to-Peer DMA (P2PDMA) between two devices requires either a shared upstream bridge or a host bridge matching pci_p2pdma_whitelist[]. 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. The P2PDMA host bridge check does not work in a Hyper-V guest. Bypass it on Intel hosts under Hyper-V, starting with Skylake-SP, the first Xeon Scalable generation. Xeon Scalable introduced UPI and is whitelisted for P2PDMA without restrictions. AMD Zen and newer are already covered by cpu_supports_p2pdma(), so the bypass is implemented for Intel hosts only. Tested with the Intel Level Zero P2P benchmark (ze_peer) on Arc Pro B60 cards in a Linux guest on Windows Server 2025 (Emerald Rapids host). Reviewed-by: Jim Chow <[email protected]> Signed-off-by: Pavel Popov <[email protected]> --- drivers/pci/p2pdma.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c index d96f44d0738a..76fadfbc1814 100644 --- a/drivers/pci/p2pdma.c +++ b/drivers/pci/p2pdma.c @@ -544,7 +544,8 @@ static bool hypervisor_supports_p2pdma(void) /* Hypervisor hides host topology, allow p2pdma on Skylake and newer */ if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL && boot_cpu_data.x86_vfm >= INTEL_SKYLAKE_X && - hypervisor_is_type(X86_HYPER_VMWARE)) + (hypervisor_is_type(X86_HYPER_VMWARE) || + hypervisor_is_type(X86_HYPER_MS_HYPERV))) return true; #endif -- 2.53.0
