Re: [PATCH v3]PCI: hv: fix PCI-BUS domainID corruption

[Sridhar Pitchai]

Hi Lorenzo,
   Transparent SRIOV is exposing the NIC directly to the kernel via
para-virtual device, unlike creating a netdev and associating it with the bond
driver. Further descriptions here,
    https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=0c195567a8f6e82ea5535cd9f1d54a1626dd233e

Previously, when using the bond driver, unique and persistent VF NIC name
was required, so we used serial number as PCI domain which is included as
part of the VF NIC name.  Transparent SRIOV mode puts VF NIC based on MAC
match as a slave of synthetic NIC, so VF NICâs name is no longer important.

Thanks,
Sridhar

ïOn 3/20/18, 11:32 AM, "Lorenzo Pieralisi" <lorenzo.pieralisi@xxxxxxx> wrote:

    On Tue, Mar 20, 2018 at 05:56:15PM +0000, Sridhar Pitchai wrote:
    > Hi Lorenzo,
    
    > Are we good with the explanation? Can I send the patch with the
    > updated commit comments?
    
    Almost.
    
    [...]
    
    >     Since we have the transparent SRIOV mode now, the short VF device name
    >     is no longer needed.
    
    Can you correlate transparent SRIOV mode to the point you are making
    below ? Please explain what transparent SRIOV mode allows you to remove
    and why. The rest of the explanation seems OK.
    
    Please follow this email format:
    
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    Thanks,
    Lorenzo
    
    >     I still do not understand what this means and how it is related to the
    >     patch below, it may be clear to you, it is not to me, at all.
    >     
    >     Sridhar >> the patch below, was introduced to make the device name small, by taking only
    >     16bits of the serial number. Since we are not going to have the serial number
    >     updated to the BUS id, this has to be removed.
    >     
    >     Fixes: 4a9b0933bdfc("PCI:hv:Use device serial number as PCI domain")
    >     
    >     Fixes: 4a9b0933bdfc ("PCI: hv: Use device serial number as PCI domain")
    >     Sridhr >> yes
    >     
    >     I asked you an explicit question. Commit above was added for a reason
    >     I assume. This patch implies that kernel has been broken since v4.11
    >     which is almost a year ago and nobody every noticed ? Or there are
    >     systems where commit above is _necessary_ and this patch would break
    >     them ?
    >     
    >     I want a detailed explanation that highlights *why* it is safe to apply
    >     this patch and send it to stable kernels, commit log above won't do.
    >     
    >     Sridhar>> HyperV provides a unique domain ID for PCI BUS. But it is modified by the child
    >     device when it is added. This cannot produce a unique domain ID all the time.
    >     Here in the bug, we see the collision between the serial number and already
    >     existing PCI bus. The cleaner way is never touch the domain ID provided by
    >     hyperV during the PCI bus creation. As long as hyperV make sure it provides a
    >     unique domain ID for the PCI for a VM it will not break, and HyperV will
    >     guarantees that the domain for the PCI bus for a given VM will be always unique.
    >     The original patch was also intending to have a unique domain ID for the PCI
    >     bus, by taking the serial number of the device, but it is not sufficient, when
    >     the device serial number is number which is the domain ID of the existing PCI
    >     bus.  With the current kernel we can repro this issue by adding a device with a
    >     serial number matching the existing PCI bus domain id. (in this case that
    >     happens to be zero).
    >     
    >     
    >     Thanks,
    >     Lorenzo
    >     
    >     Cc: stable@xxxxxxxxxxxxxxx
    >     Signed-off-by: Sridhar Pitchai <srpitcha@xxxxxxxxxxxxx>
    >     ---
    >     Changes in v3:
    >     * fix the commit comment. [KY Srinivasan, Michael Kelley]
    >     ---
    >       drivers/pci/host/pci-hyperv.c | 11 -----------
    >       1 file changed, 11 deletions(-)
    >     diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
    >     index 2faf38e..ac67e56 100644
    >     --- a/drivers/pci/host/pci-hyperv.c
    >     +++ b/drivers/pci/host/pci-hyperv.c
    >     @@ -1518,17 +1518,6 @@ static struct hv_pci_dev *new_pcichild_device(struct hv_pcibus_device *hbus,
    >       	get_pcichild(hpdev, hv_pcidev_ref_childlist);
    >       	spin_lock_irqsave(&hbus->device_list_lock, flags);
    >       
    >     -	/*
    >     -	 * When a device is being added to the bus, we set the PCI domain
    >     -	 * number to be the device serial number, which is non-zero and
    >     -	 * unique on the same VM.  The serial numbers start with 1, and
    >     -	 * increase by 1 for each device.  So device names including this
    >     -	 * can have shorter names than based on the bus instance UUID.
    >     -	 * Only the first device serial number is used for domain, so the
    >     -	 * domain number will not change after the first device is added.
    >     -	 */
    >     -	if (list_empty(&hbus->children))
    >     -		hbus->sysdata.domain = desc->ser;
    >       	list_add_tail(&hpdev->list_entry, &hbus->children);
    >       	spin_unlock_irqrestore(&hbus->device_list_lock, flags);
    >       	return hpdev;
    >     --
    >     2.7.4 
    >     
    >     
    >