Re: NVMe write protection support

[Jonathan Derrick <jonathan.derrick@linux.dev>]

On 8/25/2022 2:26 AM, Gilles Buloz wrote:
>> On Sat, Aug 06, 2022 at 10:35:00 AM +0100, Christoph Hellwig wrote:
>>   
>>> On Tue, Aug 02, 2022 at 09:20:02AM +0000, Gilles Buloz wrote:
>>> Sorry Christoph, I'm completely newbie in NVMe and don't know what "Namespace Write Protection Config" means.
>>
>> Take a look at
>> https://nvmexpress.org/wp-content/uploads/NVM-Express-Base-Specification-2.0b-2021.12.18-Ratified.pdf
>> and search for this term.
> 
> Thank you for the specs.
> 
>>> What I mean is that all the NVMe content seen by the user is write protected.
>>
>> And that is what this feature is abut.
>>
>>> Our NVMe manufacturer partner has dedicated a pin of the module for global write protection.
>>
>> There is no concept of a 'module' in NVMe.
> 
> In fact this is a M.2 module : a M.2 PCIe SSD one. A M.2 GND pin has been reused for WP with a pull-up on module, so that if the module is plugged into a standard M.2 socket this pin is connected to GND and the module is not protected. And in a socket providing WP on this pin, the write protection can be enabled by setting the pin high or unconnected.
> 
In other words, your firmware needs to set bit 0 in the ID-NS's NSATTR 
field [1] in the Identify Namespace data structure(s) when WP pin is 
grounded.


>>> But if we enable this protection and attempt a write (we should not), we get a "critical medium error" which seems a bit brutal for a disk that is still valid but just write protected. So I would like to make sure the NVMe manufacturer has used the right method/status to report this write protection, and if possible get a less fatal error feedback.
>>
>> It seems like your manufacturer needs to read the NVMe spec and implement the correct features.
> 
> Yes, that's why I requested some tips from experts like you to be sure.
> And with the features implemented correctly, is a the case of a write to a protected module already handled/expected by the kernel ? and what message the kernel is expected to report in dmesg ?
Search for 'Write Protected'/'Write Protection' in [1] spec.
You will need to support certain command Status Codes in the controller 
to convey state information on commands that may change the namespace.

[1] NVM Express Base Spec 2.0b, Figure 280
https://nvmexpress.org/wp-content/uploads/NVM-Express-Base-Specification-2.0b-2021.12.18-Ratified.pdf