Re: [PATCH v2 net] net: mvpp2: Prevent parser TCAM memory corruption

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi Tobias,

On Fri, 21 Mar 2025 10:03:23 +0100
Tobias Waldekranz <tobias@waldekranz.com> wrote:

> Protect the parser TCAM/SRAM memory, and the cached (shadow) SRAM
> information, from concurrent modifications.
> 
> Both the TCAM and SRAM tables are indirectly accessed by configuring
> an index register that selects the row to read or write to. This means
> that operations must be atomic in order to, e.g., avoid spreading
> writes across multiple rows. Since the shadow SRAM array is used to
> find free rows in the hardware table, it must also be protected in
> order to avoid TOCTOU errors where multiple cores allocate the same
> row.
> 
> This issue was detected in a situation where `mvpp2_set_rx_mode()` ran
> concurrently on two CPUs. In this particular case the
> MVPP2_PE_MAC_UC_PROMISCUOUS entry was corrupted, causing the
> classifier unit to drop all incoming unicast - indicated by the
> `rx_classifier_drops` counter.
> 
> Fixes: 3f518509dedc ("ethernet: Add new driver for Marvell Armada 375 network unit")
> Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>

I gave it a quick test with simple tcam-based vlan filtering and uc/mc
filtering, it looks and behaves fine but I probably didn't stress it
enough to hit the races you encountered. Still, the features that used
to work still work :)

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Thanks a lot,

Maxime