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SubjectRe: [PATCH v3]PCI: hv: fix PCI-BUS domainID corruption
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@vger.kernel.org
> Signed-off-by: Sridhar Pitchai <srpitcha@microsoft.com>
> ---
> 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
>
>
>

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