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That is common in passthrough guests (ESXi, Hyper-V): the > endpoint is assigned to the VM, but the guest topology has no Root > Port above it. > > 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. > > Fixes: 1ae8c4ce1570 ("PCI: Enable AtomicOps only if Root Port supports them") > Reviewed-by: Christian König > Reviewed-by: Gerd Bayer > Tested-by: Gerd Bayer > Signed-off-by: Nikola Prica CC: stable@vger.kernel.org # 7.1+ Bjorn do you want to pick that up? Alternative I can push it through drm-misc-fixes. Initially I thought that this is a new feature, but it turned out to be an regression and we need to get it fixed ASAP. Thanks, Christian. > --- > v3: Add Fixes tag > v2: Be more strict and only apply logic in headless device case. > --- > drivers/pci/pci.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index b2879a6be5f8..62729ade496f 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -3769,8 +3769,18 @@ 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 headless topology with no > + * visible root port. If it has already set AtomicOp > + * Requester Enable, there is nothing more to do. > + */ > + 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)