LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To: Sridhar Pitchai <Sridhar.Pitchai@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Michael Kelley \(EOSG\)" <Michael.H.Kelley@microsoft.com>,
	Jake Oshins <jakeo@microsoft.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	"devel@linuxdriverproject.org" <devel@linuxdriverproject.org>
Subject: Re: [PATCH v3]PCI: hv: fix PCI-BUS domainID corruption
Date: Tue, 20 Mar 2018 18:32:08 +0000	[thread overview]
Message-ID: <20180320183208.GB24991@e107981-ln.cambridge.arm.com> (raw)
In-Reply-To: <65B4E847-CC40-4166-BE8F-D44049EDB2FF@microsoft.com>

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 
>     
>     
> 
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel

  reply	other threads:[~2018-03-20 18:32 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-15  0:03 Sridhar Pitchai
2018-03-15 12:05 ` Lorenzo Pieralisi
2018-03-15 17:56   ` Sridhar Pitchai
2018-03-15 18:24     ` Sridhar Pitchai
2018-03-20 17:56       ` Sridhar Pitchai
2018-03-20 18:32         ` Lorenzo Pieralisi [this message]
2018-03-20 23:00           ` Sridhar Pitchai
2018-03-21 16:26             ` Lorenzo Pieralisi
2018-03-23 16:41               ` Sridhar Pitchai
2018-03-23 16:47                 ` Greg KH
2018-03-26 17:32                   ` Sridhar Pitchai
2018-03-21 17:30             ` Bjorn Helgaas
2018-03-23 16:09               ` Sridhar Pitchai

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180320183208.GB24991@e107981-ln.cambridge.arm.com \
    --to=lorenzo.pieralisi@arm.com \
    --cc=Michael.H.Kelley@microsoft.com \
    --cc=Sridhar.Pitchai@microsoft.com \
    --cc=bhelgaas@google.com \
    --cc=devel@linuxdriverproject.org \
    --cc=haiyangz@microsoft.com \
    --cc=jakeo@microsoft.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pci@vger.kernel.org \
    --cc=sthemmin@microsoft.com \
    --subject='Re: [PATCH v3]PCI: hv: fix PCI-BUS domainID corruption' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).