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

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Date:   Thu, 28 Feb 2019 17:30:26 -0700
From:   Keith Busch <kbusch@...nel.org>
To:     Austin.Bolen@...l.com
Cc:     hch@...radead.org, Alex_Gagniuc@...lteam.com,
        torvalds@...ux-foundation.org, keith.busch@...el.com,
        sagi@...mberg.me, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, axboe@...com, mr.nuke.me@...il.com,
        hch@....de, jonathan.derrick@...el.com
Subject: Re: [PATCH] nvme-pci: Prevent mmio reads if pci channel offline

On Thu, Feb 28, 2019 at 11:43:46PM +0000, Austin.Bolen@...l.com wrote:
> On 2/28/2019 5:20 PM, Keith Busch wrote:
> > SBR and Link Disable are done from the down stream port, though, so the
> > host can still communicate with the function that took the link down.
> > That's entirely different than taking the link down from the end device,
> > so I'm not sure how NVMe can fix that.
> > 
> 
> Agreed it is different.  Here is one way they could have solved it: host 
> writes magic value to NSSRC but device latches this instead of 
> resetting.  Then require host to do SBR.  When device sees SBR with 
> magic value in NSSRC it does an NSSR.

For single port drives, yes, but that wouldn't work so well for multi-port
devices connected to different busses, maybe even across multiple hosts.
The equivalent of an FLR across all ports should have been sufficient,
IMO.