linux-kernel - RE: [Patch v2] PCI: hv: Fix NUMA node assignment when kernel boots with custom NUMA topology

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Message-ID: <CY4PR21MB1586368DF27F62BBFA12F2BCD7599@CY4PR21MB1586.namprd21.prod.outlook.com>
Date:   Wed, 19 Jan 2022 04:40:20 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     "longli@...uxonhyperv.com" <longli@...uxonhyperv.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        Purna Pavan Chandra Aekkaladevi <paekkaladevi@...rosoft.com>
CC:     Long Li <longli@...rosoft.com>
Subject: RE: [Patch v2] PCI: hv: Fix NUMA node assignment when kernel boots
 with custom NUMA topology

From: longli@...uxonhyperv.com <longli@...uxonhyperv.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@...rosoft.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@...rosoft.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