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Date: Fri, 27 Apr 2018 09:09:43 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: Sinan Kaya <okaya@codeaurora.org>
Cc: stable@vger.kernel.org, Keith Busch <keith.busch@intel.com>,
        Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: Please apply commit 821cdad5c46c to v4.9.y
Message-ID: <20180427070943.GD4931@kroah.com>
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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