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SubjectRE: [Patch v2] PCI: hv: Fix NUMA node assignment when kernel boots with custom NUMA topology
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From: longli@linuxonhyperv.com <longli@linuxonhyperv.com> Sent: Tuesday, January 18, 2022 6:45 PM
>
> When kernel boots with a NUMA topology with some NUMA nodes offline, the PCI
> driver should only set an online NUMA node on the device. This can happen
> during KDUMP where some NUMA nodes are not made online by the KDUMP kernel.
>
> This patch also fixes the case where kernel is booting with "numa=off".
>
> Signed-off-by: Long Li <longli@microsoft.com>

It seems like adding a "Fixes:" tag would be appropriate.

>
> Change from v1:
> Use numa_map_to_online_node() to assign a node to device (suggested by
> Michael Kelly <mikelley@microsoft.com>)
>
> ---
> drivers/pci/controller/pci-hyperv.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index 6c9efeefae1b..c7519add6f13 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -2130,7 +2130,15 @@ static void hv_pci_assign_numa_node(struct
> hv_pcibus_device *hbus)
> continue;
>
> if (hv_dev->desc.flags & HV_PCI_DEVICE_FLAG_NUMA_AFFINITY)
> - set_dev_node(&dev->dev, hv_dev->desc.virtual_numa_node);
> + /*
> + * The kernel may boot with some NUMA nodes offline
> + * (e.g. in a KDUMP kernel) or with NUMA disabled via
> + * "numa=off". In those cases, adjust the host provided
> + * NUMA node to a valid NUMA node used by the kernel.
> + */
> + set_dev_node(&dev->dev,
> + numa_map_to_online_node(
> + hv_dev->desc.virtual_numa_node));

Double-check me, but I think this approach has a flaw in that
numa_map_to_online_node() doesn't check the input node for being
out-of-range. The call to node_online() uses the input node to index into
the node_states bitmap (of type nodemask_t), and could go off the end of
the bitmap if the input node isn't validated to be less than MAX_NUMNODES
(or nr_node_ids).

Michael

>
> put_pcichild(hv_dev);
> }
> --
> 2.25.1

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