Re: [PATCH] nvme-pci: Prevent mmio reads if pci channel offline

[Christoph Hellwig <hch@infradead.org>]

On Wed, Feb 27, 2019 at 08:04:35PM +0000, Austin.Bolen@dell.com wrote:
> Confirmed this issue does not apply to the referenced Dell servers so I 
> don't not have a stake in how this should be handled for those systems. 
> It may be they just don't support surprise removal.  I know in our case 
> all the Linux distributions we qualify (RHEL, SLES, Ubuntu Server) have 
> told us they do not support surprise removal.  So I'm guessing that any 
> issues found with surprise removal could potentially fall under the 
> category of "unsupported".
> 
> Still though, the larger issue of recovering from other types of PCIe 
> errors that are not due to device removal is still important.  I would 
> expect many system from many platform makers to not be able to recover 
> PCIe errors in general and hopefully the new DPC CER model will help 
> address this and provide added protection for cases like above as well.

FYI, a related issue I saw about a year two ago with Dell servers was
with a dual ported NVMe add-in (non U.2) card, is that once you did
a subsystem reset, which would cause both controller to retrain the link
you'd run into Firmware First error handling issue that would instantly
crash the system.  I don't really have the hardware anymore, but the
end result was that I think the affected product ended up shipping
with subsystem resets only enabled for the U.2 form factor.