From 40cce45b921f7930886bcba43069edc579725457 Mon Sep 17 00:00:00 2001 From: Nikola Prica Date: Mon, 21 Sep 2026 13:19:03 +0200 Subject: PCI: Accept AtomicOps already enabled by the hypervisor MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit pci_enable_atomic_ops_to_root() currently fails when no Root Port is visible. That is common in passthrough guests (ESXi, Hyper-V): the Endpoint is assigned to the VM, but the Root Port above it is not visible in the guest topology. In those setups the hypervisor may already have enabled AtomicOp Requester Enable on the device. If PCI_EXP_DEVCTL2_ATOMIC_REQ is set, treat AtomicOps as already enabled and return success instead of failing the Root Port walk. After 1ae8c4ce1570 ("PCI: Enable AtomicOps only if Root Port supports them"), pci_enable_atomic_ops_to_root() always returns failure if the Root Port is not visible, so drivers don't use atomics when they could. On systems where the Root Port is not visible but *does* support AtomicOps, this is a regression: prior to 1ae8c4ce1570, it enabled AtomicOps in the endpoint and returned success. Fixes: 1ae8c4ce1570 ("PCI: Enable AtomicOps only if Root Port supports them") Signed-off-by: Nikola Prica [bhelgaas: commit log, code comment] Signed-off-by: Bjorn Helgaas Tested-by: Gerd Bayer Reviewed-by: Christian König Reviewed-by: Gerd Bayer Link: https://patch.msgid.link/20260921111903.978687-1-nikprica@amd.com --- drivers/pci/pci.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) (limited to 'drivers') diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index b2879a6be..8cc6a8913 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -3769,8 +3769,21 @@ int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask) } root = pcie_find_root_port(dev); - if (!root) + if (!root) { + + /* + * A hypervisor may expose a topology with the root port + * not visible to the guest. If the hypervisor has already + * set AtomicOp Requester Enable in the endpoint, we assume + * it has verified support in the root port, so it is safe + * for the driver to use AtomicOps. + */ + pcie_capability_read_dword(dev, PCI_EXP_DEVCTL2, &ctl2); + if (ctl2 & PCI_EXP_DEVCTL2_ATOMIC_REQ) + return 0; + return -EINVAL; + } pcie_capability_read_dword(root, PCI_EXP_DEVCAP2, &cap); if ((cap & cap_mask) != cap_mask) -- cgit v1.3.1