netdev - RE: Re: [PATCH] net: ena: Add PCI shutdown handler to allow safe kexec

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Date:   Wed, 25 Mar 2020 09:08:41 +0000
From:   "Jubran, Samih" <sameehj@...zon.com>
To:     David Miller <davem@...emloft.net>,
        "gpiccoli@...onical.com" <gpiccoli@...onical.com>
CC:     "Belgazal, Netanel" <netanel@...zon.com>,
        "Kiyanovski, Arthur" <akiyano@...zon.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Tzalik, Guy" <gtzalik@...zon.com>,
        "Bshara, Saeed" <saeedb@...zon.com>,
        "Machulsky, Zorik" <zorik@...zon.com>,
        "kernel@...ccoli.net" <kernel@...ccoli.net>,
        "gshan@...hat.com" <gshan@...hat.com>,
        "gavin.guo@...onical.com" <gavin.guo@...onical.com>,
        "jay.vosburgh@...onical.com" <jay.vosburgh@...onical.com>,
        "pedro.principeza@...onical.com" <pedro.principeza@...onical.com>
Subject: RE: Re: [PATCH] net: ena: Add PCI shutdown handler to allow safe
 kexec



> -----Original Message-----
> From: Jubran, Samih
> Sent: Tuesday, March 24, 2020 7:03 PM
> To: 'David Miller' <davem@...emloft.net>; 'gpiccoli@...onical.com'
> <gpiccoli@...onical.com>
> Cc: Belgazal, Netanel <netanel@...zon.com>; Kiyanovski, Arthur
> <akiyano@...zon.com>; 'netdev@...r.kernel.org'
> <netdev@...r.kernel.org>; Tzalik, Guy <gtzalik@...zon.com>; Bshara,
> Saeed <saeedb@...zon.com>; Machulsky, Zorik <zorik@...zon.com>;
> 'kernel@...ccoli.net' <kernel@...ccoli.net>; 'gshan@...hat.com'
> <gshan@...hat.com>; 'gavin.guo@...onical.com'
> <gavin.guo@...onical.com>; 'jay.vosburgh@...onical.com'
> <jay.vosburgh@...onical.com>; 'pedro.principeza@...onical.com'
> <pedro.principeza@...onical.com>
> Subject: RE: Re: [PATCH] net: ena: Add PCI shutdown handler to allow safe
> kexec
> 
> 
> 
> > -----Original Message-----
> > From: netdev-owner@...r.kernel.org <netdev-owner@...r.kernel.org>
> On
> > Behalf Of David Miller <davem@...emloft.net>
> > Sent: Tuesday, March 24, 2020 6:05 AM
> > To: gpiccoli@...onical.com
> > Cc: netanel@...zon.com; akiyano@...zon.com;
> netdev@...r.kernel.org;
> > gtzalik@...zon.com; saeedb@...zon.com; zorik@...zon.com;
> > kernel@...ccoli.net; gshan@...hat.com; gavin.guo@...onical.com;
> > jay.vosburgh@...onical.com; pedro.principeza@...onical.com
> > Subject: Re: [PATCH] net: ena: Add PCI shutdown handler to allow safe
> > kexec
> >
> > From: "Guilherme G. Piccoli" <gpiccoli@...onical.com>
> > Date: Fri, 20 Mar 2020 09:55:34 -0300
> >
> > > Currently ENA only provides the PCI remove() handler, used during
> > > rmmod for example. This is not called on shutdown/kexec path; we are
> > > potentially creating a failure scenario on kexec:
> > >
> > > (a) Kexec is triggered, no shutdown() / remove() handler is called
> > > for ENA; instead pci_device_shutdown() clears the master bit of the
> > > PCI device, stopping all DMA transactions;
> > >
> > > (b) Kexec reboot happens and the device gets enabled again, likely
> > > having its FW with that DMA transaction buffered; then it may
> > > trigger the (now
> > > invalid) memory operation in the new kernel, corrupting kernel
> > > memory
> > area.
> > >
> > > This patch aims to prevent this, by implementing a shutdown()
> > > handler quite similar to the remove() one - the difference being the
> > > handling of the netdev, which is unregistered on remove(), but
> > > following the convention observed in other drivers, it's only detached on
> shutdown().
> > >
> > > This prevents an odd issue in AWS Nitro instances, in which after
> > > the 2nd kexec the next one will fail with an initrd corruption,
> > > caused by a wild DMA write to invalid kernel memory. The lspci
> > > output for the adapter present in my instance is:
> > >
> > > 00:05.0 Ethernet controller [0200]: Amazon.com, Inc. Elastic Network
> > > Adapter (ENA) [1d0f:ec20]
> > >
> > > Suggested-by: Gavin Shan <gshan@...hat.com>
> > > Signed-off-by: Guilherme G. Piccoli <gpiccoli@...onical.com>
> >
> > Amazon folks, please review.
> 
> The patch is still under review we will reply as soon as we have finished
> testing it, Thanks

Acked-by: Sameeh Jubran <sameehj@...zon.com>