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

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Message-Id: <20200323.210444.2145186350378871245.davem@davemloft.net>
Date:   Mon, 23 Mar 2020 21:04:44 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
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.