linux-kernel - Re: [PATCH] xen: xen-pciback: Export a bridge and all its children as per TODO

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Date: Mon, 10 Jun 2024 09:49:48 +0200
From: Jan Beulich <jbeulich@...e.com>
To: Abhinav Jain <jain.abhinav177@...il.com>
Cc: skhan@...uxfoundation.org, javier.carrasco.cruz@...il.com,
 jgross@...e.com, sstabellini@...nel.org, oleksandr_tyshchenko@...m.com,
 xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen: xen-pciback: Export a bridge and all its children as
 per TODO

On 09.06.2024 20:44, Abhinav Jain wrote:
> Check if the device is a bridge.
> If it is a bridge, iterate over all its child devices and export them.
> Log error if the export fails for any particular device logging details.
> Export error string is split across lines as I could see several
> other such occurrences in the file.
> Please let me know if I should change it in some way.
> 
> Signed-off-by: Abhinav Jain <jain.abhinav177@...il.com>
> ---
>  drivers/xen/xen-pciback/xenbus.c | 39 +++++++++++++++++++++++++-------
>  1 file changed, 31 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c
> index b11e401f1b1e..d15271d33ad6 100644
> --- a/drivers/xen/xen-pciback/xenbus.c
> +++ b/drivers/xen/xen-pciback/xenbus.c
> @@ -258,14 +258,37 @@ static int xen_pcibk_export_device(struct xen_pcibk_device *pdev,
>  		xen_register_device_domain_owner(dev, pdev->xdev->otherend_id);
>  	}
>  
> -	/* TODO: It'd be nice to export a bridge and have all of its children
> -	 * get exported with it. This may be best done in xend (which will
> -	 * have to calculate resource usage anyway) but we probably want to
> -	 * put something in here to ensure that if a bridge gets given to a
> -	 * driver domain, that all devices under that bridge are not given
> -	 * to other driver domains (as he who controls the bridge can disable
> -	 * it and stop the other devices from working).
> -	 */
> +	/* Check if the device is a bridge and export all its children */
> +	if ((dev->hdr_type && PCI_HEADER_TYPE_MASK) == PCI_HEADER_TYPE_BRIDGE) {

Besides it wanting to be & here, it feels as if such a change can't be done
standalone in pciback. It likely needs adjustments in the tool stack (even
if that's not send anymore) and possibly also arrangements in the hypervisor
(to correctly deal with bridges when handed to other than Dom0).

> +		struct pci_dev *child = NULL;
> +
> +		/* Iterate over all the devices in this bridge */
> +		list_for_each_entry(child, &dev->subordinate->devices,
> +				bus_list) {
> +			dev_dbg(&pdev->xdev->dev,
> +				"exporting child device %04x:%02x:%02x.%d\n",
> +				child->domain, child->bus->number,
> +				PCI_SLOT(child->devfn),
> +				PCI_FUNC(child->devfn));
> +
> +			err = xen_pcibk_export_device(pdev,
> +						      child->domain,
> +						      child->bus->number,
> +						      PCI_SLOT(child->devfn),
> +						      PCI_FUNC(child->devfn),
> +						      devid);
> +			if (err) {
> +				dev_err(&pdev->xdev->dev,
> +					"failed to export child device : "
> +					"%04x:%02x:%02x.%d\n",
> +					child->domain,
> +					child->bus->number,
> +					PCI_SLOT(child->devfn),
> +					PCI_FUNC(child->devfn));
> +				goto out;

Hmm, and leaving things in partially-exported state?

Jan

> +			}
> +		}
> +	}
>  out:
>  	return err;
>  }