linux-kernel - Re: [PATCH net-next v9 2/9] net: add get_netmem/put

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Message-ID: <957b74ed-f29c-4bb8-b819-af4e1168d6c1@gmail.com>
Date: Tue, 22 Apr 2025 19:20:59 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Mina Almasry <almasrymina@...gle.com>
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Subject: Re: [PATCH net-next v9 2/9] net: add get_netmem/put_netmem support

On 4/22/25 14:56, Mina Almasry wrote:
> On Tue, Apr 22, 2025 at 1:43 AM Pavel Begunkov <asml.silence@...il.com> wrote:
>>
>> On 4/18/25 00:15, Mina Almasry wrote:
>>> Currently net_iovs support only pp ref counts, and do not support a
>>> page ref equivalent.
>>
>> Makes me wonder why it's needed. In theory, nobody should ever be
>> taking page references without going through struct ubuf_info
>> handling first, all in kernel users of these pages should always
>> be paired with ubuf_info, as it's user memory, it's not stable,
>> and without ubuf_info the user is allowed to overwrite it.
>>
> 
> The concern about the stability of the from-userspace data is already
> called out in the MSG_ZEROCOPY documentation that we're piggybacking
> devmem TX onto:

Sure, I didn't object that. There is no problem as long as the
ubuf_info semantics is followed, which by extension mean that
any ref manipulation should already be gated on ubuf_info, and
there should be no need in changing generic paths.

-- 
Pavel Begunkov