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: http://vger.kernel.org/lkml/#s3-9 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 > > > _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
