linux-kernel - Re: [PATCH] pci: add NVMe FLR quirk to the SM951 SSD

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Date:   Wed, 19 May 2021 09:44:08 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Robert Straw <drbawb@...alsyntax.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, bhelgaas@...gle.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH] pci: add NVMe FLR quirk to the SM951 SSD

On Sat, May 15, 2021 at 12:20:05PM -0500, Robert Straw wrote:
> On page 40, sec 3.1.6 of the NVMe 1.1 spec, the documentation on SHST 
> states the following:

While it doesn't matter here, NVMe 1.1 is very much out of data, being
a more than 8 year old specification.  The current version is 1.4b,
with NVMe 2.0 about to be released.

> Knowing this I would suspect we'd actually want to treat most NVMe
> drives in this manner *if the kernel sees the SHN/SHST has been set
> prior.* Perhaps other NVMe devices are more tolerant of not doing this?

No, we don't.  This is a bug particular to a specific implementation.
In fact the whole existing NVMe shutdown before reset quirk is rather
broken and dangerous, as it concurrently accesses the NVMe registers
with the actual driver, which could be trivially triggered through the
sysfs reset attribute.

I'd much rather quirk these broken Samsung drivers to not allow
assigning them to VFIO.