netdev - Re: [PATCH net-next v6 02/19] psp: base PSP device support

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Message-ID: <3c36afe7-de39-4fff-80ae-e615b5189f67@redhat.com>
Date: Thu, 14 Aug 2025 17:46:37 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Daniel Zahka <daniel.zahka@...il.com>,
 Donald Hunter <donald.hunter@...il.com>, Jakub Kicinski <kuba@...nel.org>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>,
 Andrew Lunn <andrew+netdev@...n.ch>
Cc: Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
 Tariq Toukan <tariqt@...dia.com>, Boris Pismenny <borisp@...dia.com>,
 Kuniyuki Iwashima <kuniyu@...gle.com>, Willem de Bruijn
 <willemb@...gle.com>, David Ahern <dsahern@...nel.org>,
 Neal Cardwell <ncardwell@...gle.com>, Patrisious Haddad
 <phaddad@...dia.com>, Raed Salem <raeds@...dia.com>,
 Jianbo Liu <jianbol@...dia.com>, Dragos Tatulea <dtatulea@...dia.com>,
 Rahul Rameshbabu <rrameshbabu@...dia.com>,
 Stanislav Fomichev <sdf@...ichev.me>,
 Toke Høiland-Jørgensen <toke@...hat.com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>,
 Kiran Kella <kiran.kella@...adcom.com>,
 Jacob Keller <jacob.e.keller@...el.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v6 02/19] psp: base PSP device support

On 8/14/25 5:14 PM, Daniel Zahka wrote:
> On 8/14/25 10:21 AM, Paolo Abeni wrote:
>> On 8/12/25 2:29 AM, Daniel Zahka wrote:
>>> +/**
>>> + * psp_dev_unregister() - unregister PSP device
>>> + * @psd:	PSP device structure
>>> + */
>>> +void psp_dev_unregister(struct psp_dev *psd)
>>> +{
>>> +	mutex_lock(&psp_devs_lock);
>>> +	mutex_lock(&psd->lock);
>>> +
>>> +	psp_nl_notify_dev(psd, PSP_CMD_DEV_DEL_NTF);
>>> +	xa_store(&psp_devs, psd->id, NULL, GFP_KERNEL);
>> It's not 110% obvious to me that the above is equivalent to xa_clear(),
>> given the XA_FLAGS_ALLOC1 init flag. If you have to re-submit, please
>> consider using xa_clear() instead.
> 
> This was actually a deliberate decision to use xa_store() with NULL in 
> psp_dev_unregister(), and then call xa_erase() after from 
> psp_dev_destroy(). psp_dev_unregister() is called synchronously by 
> drivers to uniniatialize psp, whereas psp_dev_destroy() is called once 
> the refcount of a psp_dev goes to 0. A system could have multiple psp 
> NICs, in which case policy checks at the socket layer need to compare 
> the pair of (spi, psp dev id), as opposed to just the spi.
> 
> What we were going for with this decision was to try and prevent an 
> attacker from trying to quickly trigger or wait for 
> psp_dev_unregister(), and then try to bring up a new psp device with the 
> same psp_dev id, while a socket may still be holding a reference to the 
> old psp device. So we delay calling xa_erase() until after all 
> references to the old psp_dev are gone to release the id (xa_array slot).
> 
> Perhaps I can add a comment, because I can see how that would trip up 
> readers.

Indeed the above was completely unobvious to me, and definitely a
comment could help long term maintenance.

Thanks,

Paolo