Please apply commit 821cdad5c46c to v4.9.y

Please apply commit 821cdad5c46c to v4.9.y

[Sinan Kaya]

Hi Greg,

Upstream commit 821cdad5c46c ("PCI: Wait up to 60 seconds for
device to become ready after FLR") fixes a virtualization issue
for Intel 750 NVMe drive and potentially other PCIe devices taking
longer to recover from functional resets.

problem description below from the commit:

'Sporadic reset issues have been observed with an Intel 750 NVMe drive while
assigning the physical function to the guest machine.  The sequence of
events observed is as follows:

- perform a Function Level Reset (FLR)
- sleep up to 1000ms total
- read ~0 from PCI_COMMAND (CRS completion for config read)
- warn that the device didn't return from FLR
- touch the device before it's ready
- device drops config writes when we restore register settings (there's
  no mechanism for software to learn about CRS completions for writes)
- incomplete register restore leaves device in inconsistent state
- device probe fails because device is in inconsistent state

After reset, an endpoint may respond to config requests with Configuration
Request Retry Status (CRS) to indicate that it is not ready to accept new
requests. See PCIe r3.1, sec 2.3.1 and 6.6.2.'

Please apply commit 821cdad5c46c to fix the resulting regression.

Thanks,
Sinan

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

Re: Please apply commit 821cdad5c46c to v4.9.y

[Greg KH]

On Thu, Apr 26, 2018 at 04:34:50PM -0400, Sinan Kaya wrote:
> Hi Greg,
> 
> Upstream commit 821cdad5c46c ("PCI: Wait up to 60 seconds for
> device to become ready after FLR") fixes a virtualization issue
> for Intel 750 NVMe drive and potentially other PCIe devices taking
> longer to recover from functional resets.
> 
> problem description below from the commit:
> 
> 'Sporadic reset issues have been observed with an Intel 750 NVMe drive while
> assigning the physical function to the guest machine.  The sequence of
> events observed is as follows:
> 
> - perform a Function Level Reset (FLR)
> - sleep up to 1000ms total
> - read ~0 from PCI_COMMAND (CRS completion for config read)
> - warn that the device didn't return from FLR
> - touch the device before it's ready
> - device drops config writes when we restore register settings (there's
>   no mechanism for software to learn about CRS completions for writes)
> - incomplete register restore leaves device in inconsistent state
> - device probe fails because device is in inconsistent state
> 
> After reset, an endpoint may respond to config requests with Configuration
> Request Retry Status (CRS) to indicate that it is not ready to accept new
> requests. See PCIe r3.1, sec 2.3.1 and 6.6.2.'
> 
> Please apply commit 821cdad5c46c to fix the resulting regression.

Looks good, but it's not really a "regression" as it didn't work at all
before this patch :)

Now queued up.

greg k-h