lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Tue, 16 Sep 2014 09:40:49 -0600
From:	Bjorn Helgaas <>
To:	Rajat Jain <>
Cc:	"" <>,
	"" <>,
	Rajat Jain <>,
	Guenter Roeck <>,
	Linus Torvalds <>,
	Richard Yang <>,
	Matthew Wilcox <>,
	Yinghai Lu <>,
	Josh Logan <>
Subject: Re: [PATCH v2] pci/probe: Enable CRS for root port if it is supported

On Mon, Sep 15, 2014 at 10:10:20PM -0700, Rajat Jain wrote:
> Hi Bjorn,
> On Mon, Sep 8, 2014 at 10:38 PM, Bjorn Helgaas <> wrote:
> > On Tue, Sep 02, 2014 at 04:26:00PM -0700, Rajat Jain wrote:
> >>
> >> As per the PCIe spec, an endpoint may return the configuration cycles
> >> with CRS if it is not yet fully ready to be accessed. If the CRS visibility
> >> is not enabled at the root port, the spec leaves the retry behaviour open
> >> to implementation in such a case. The Intel root ports have chosen to retry
> >> endlessly in this situation. Thus, the root controller may "hang" (repeatedly
> >> retrying the configuration requests until it gets a status other than CRS) if
> >> a device returns CRS for a long time. This can cause a broken endpoint to bring
> >> down the whole PCI hierarchy.
> >>
> >> This was recently known to cause problems on Intel systems and
> >> was discussed here:
> >>
> >>
> >> Ref1:
> >>
> >>
> >> Ref2:
> >> PCIe spec V3.0, pg119, pg127 for "Configuration Request Retry Status"
> >>
> >> Thus enable the CRS visibility for the root ports that support it. This
> >> patch reverts the following commit, but enables CRS visibility only
> >> when the root port supports it:
> >>
> >> ad7edfe04908 ("[PCI] Do not enable CRS Software Visibility by default")
> >>
> >> (Linus' response:
> >>
> >> Signed-off-by: Rajat Jain <>
> >> Signed-off-by: Rajat Jain <>
> >> Signed-off-by: Guenter Roeck <>
> >
> > I put this and the "only look at Vendor ID" patch on a pci/enumeration
> > branch [1].  I rewrote the changelogs to reflect my understanding of what's
> > going on, so probably the real truth is somewhere between your original and
> > mine.  Let me know what should be fixed.
> >
> > We should figure out an easy way for Josh to test these.  Ideally, he could
> > test the second patch by itself first, then both together.
> OK, Josh and I tested this over the last week on his HW (the HW that
> had originally reported the problem). Somehow his hardware does not
> show the problem in ANY case. I tried the following, and the original
> issue (vendor id = 1) was never seen:
> 1) 3.17-rc2 (has CRS disabled)
> 2) 3.17-rc2 + Enable CRS
> 3) 3.17-rc2 + Enable CRS + Ignore Device ID
> The Device always returned the correct Vendor ID and Device ID in all
> cases. Thus even enabling CRS does not make his system fail in anyway.

Thanks a lot for all the work to dig out the board and test it.  I really
appreciate it.

My inclination is to apply both patches.  It doesn't seem strictly
necessary to ignore the device ID on this platform, but I don't think we
gain anything by verifying that device ID == 0xffff except confirming spec

We *could* put more effort into reproducing the original problem, e.g.,
by building v2.6.24-rc1, where this problem was originally reported, and
(hopefully) reproducing it there, then figuring out where it got fixed
along the way.  But I'm not sure it's worth the effort.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists